Check the milling. The reason something is half price and ready to go is usually because it is defective or seconds.

Is this a good deal being that it still needs to be sanded and site finished?

That price seems quite reasonable

What are the pros/cons to site finished engineered hardwood. Generally speaking, what makes the pre-finished hardwood so much more durable against scratches?

Pros are that job finishing can give you the exact color, finish and sheen you choose and there's finish applied across the top so it might protect a little better from surface moisture. The cons are generally the cost and amount of time it takes. Prefinished floors generally have aluminum oxide added to the finish which is demonstrably better for durability.

Will a micro bevel trap less dirt if site finished?

Only if your house is a pigpen. I suspect it's not. At my old office/showroom we got a lot of dirt tracked in due to being on a busy highway and the French parquet patterns with deep bevels never had any issue with getting dirty.

Is a square bevel superior to a micro bevel or just personal preference?

Personal preference mostly, but smooth will providing a seamless flowing look where a bevel will highlight the floor more and potentially help hide wear over the longer term.

No such thing as a free lunch? Factory finished is almost always better. Almost...plus it should have a wear warranty? As for bevel.. I hate(yes I used the H word) how dirt gets trapped. Personally, in all of my specs, i use floating floor, pre finished. That's my 2 cents

There is just so much to learn so I greatly appreciate everyone’s amazing advice!