I don't have one but in reading the description, here are some things I would consider.
It looks like it "fits" on the burners which might make it more stable.
It is coated with porcelain so it would not take a seasoning. The chef king can be seasoned to become non stick like cast iron. Sometimes porcelain can have issues with chipping or popping.
Another alternative but one that no one has reviewed, here is an uncoated aluminum griddle by royal Industries. It will take a seasoning although not quite as easily as a cast iron or steel one will. It is lighter in weight and conducts heat much better than the steel ones. This makes it much more responsive if you have to turn it up or down. It heats more evenly. It is the same thickness as the Chef King. The steel will hold more heat though. I like the shape of the Chef King because it just seems like it would be easier to clean.

I have an bare aluminum griddle that fit on my old range and is too small for the one now. It is great and even though it doesn't fit the stove, it still heats evenly. I also have a non stick griddle(aluminum) that fits the range now and it will toast sandwiches perfectly even wall to wall. I am not a big fan of the "nonstick" though. Unfortunately almost all of the aluminum griddles are non stick except the Royal.

Here is a link that might be useful: Royal Aluminum Griddle

I don't know about the Bluestar, but if it's cast iron and that large, it's bound to be heavy- probably not too heavy. Also, porcelain will take a seasoning- just like the burner grates.

I have several griddles (actually 3).
#1 is 1/4" thick carbon steel- it's big and heavy and has a stainless housing to hold it and a drip tray at one end. American range made it- expensive.

#2 is thick aluminum with a good non-stick finish- it was maybe $80 and has a shallow drip tray around the perimeter- that unfortunately takes up surface space

#3 looks like the bluestar only is wider (14") x24 and is also aluminum/ non-stick. It's width allows for bigger pancakes! I think Jade made it- expensive- I think they make several models and sizes- I bought the largest.
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But #2 is the one I use all the time. It works great and spreads the heat evenly- covers two burners and is easy to use and clean and store. It's the chefs design maxi griddle. Like I said before, I wish it had a smaller drip channel. IT IS also available without the non-stick coating.

I do have a french grill plate that is porcelain cast iron- mine is square and covers only 1 burner- takes longer to heat than aluminum. Le Creuset also makes a Cast Iron 'Bistro Grill Pan', 12-2/3-Inch - round.

Really the 'best' depends on what you use it for. If it's pancakes , I think aluminum does a better job- more even heating. If it's eggs and bacon or melted cheese sandwiches, I don't think it matters much.

Here is a link that might be useful: maxi griddle

My experience with porcelain has been with two Le Creuset skillets with a matte black enamel interior, that from the website " Over time, the matte black interior enamel develops a natural patina that is ideal for searing and frying". I never could get a nonstick surface like you can with cast iron. Maybe I just wasn't patient enough but I got rid of them after a year. They just seemed to stick more than even the regular Le Creuset. I also have about a dozen other pieces of enameled cast iron, vintage, made in France of various brands that have not seasoned either to the point of being nonstick. Maybe BS is different and someone who has the BS griddle can give their experience.

The only reason I don't like the nonstick is that eventually they will degrade and you can't use high heat. The speed at which this happens will depend on the amount of heat you use and how careful you are with it. We have a local cook in our town that has nonstick all-clad that is 30 years old and looks brand new, but I have never had nonstick last more than about 4 years.

This the griddle I have. It came with a previous appliance. It works great but I don't expect it to last all that long. I would never spend $289 on something like this.

Here is a link that might be useful: Nonstick griddle

It really is hard to push the button to buy when not many have had experience.
I have a couple that are cast iron and well seasoned. And inexpensive.
(one in a vacation home)

I did consider this one as it appears to be a good 'add-on' but i stumbled over the cost.

Here is a link that might be useful: portable grill plate

hey sleevendog, i actually have that add-on griddle you show in the link. i don't use it that often though. first, it's VERY heavy. and second, it's stainless steel, and not yet seasoned enough to get eggs to slide right off without sticking.

although, perhaps the main reason for it's lack of use is that i have 6 burners on my Bluestar, and that's plenty to make even huge breakfasts for multiple people just using various pans.

Here is a video on quick seasoning of stainless and discussion. It might work on the porcelain too. On another thread some people liked the fact that steel and cast iron did not heat as evenly as aluminum because they liked having areas on the cooking surface that were not as hot.

Here is a link that might be useful: Seasoning stainless

I have been using LeCrueset's porcelain coated cast iron grill/griddle for years on my four burner Whirlpool. I use a griddle every day so it is worth keeping out for me. I'm just about done planning my remodel(now I'm figuring out lighting) but when looking at appliances I couldn't decide to do a built in griddle or keep a separate one. I just decided to buy the Chef King and if I hated it I was only out $50. I now love it and use it every day instead of the old one. I would not pay such high price for Blue Star's model which is basically the same material as LeCrueset. You can't build up any kind of finish on it because its coated. Not to mention that eventually it will chip as mine has. Probably in several years, but it will. FWIW, I am going with BS 36" six burner rangetop.
I really value things fitting well, and the allure of this plate fitting exactly over the burners can't be denied. I took Wekick's advice of the Chef King, but if you want cast iron, get the Lodge LPG13 that is roughly 11x20. It's about $35-$50 depending on where you buy. Its uncoated and you can build up a good finish on it. I would strip it of the factory 'pre-seasoning' first. If you can try them out before you demo, I would consider that money well spent. HTH

Just to mention, those looking into a new range/rangetop. I have the built in griddle on my 36" Bluestar and I use it just as often as the burners, if not more! ...at least once every day, and often two or three times... it has developed a beautiful non stick seasoning that even eggs slide right off.

still here, and using that griddle! Mine heats to breakfast/ grilled sandwich temp (325+-) in about seven or eight minutes... and a few minutes more to searing hot...maybe your thermostat needs adjusting?
Greasy diner style burgers just the other night ;)

I bought the Chef's Design 11 by 19 1/2 inch about $60, but it works great, and it fits my 30 inch RNB very well - though I usually use on the front burner, and use the rear to stack the pancakes that have been cooked. If you check the reviews, you will see that nearly all are glowing.

Here is a link that might be useful: amazon