Funny pipe and flexible PVC are two different products. Funny pipe is connected using barbed fittings and flexible PVC is solvent welded using a "hot" PVC cement.
I'm no fan of any type of flexible pipe in a residential irrigation system. Funny pipe isn't durable enough and has a propensity to leak at the barbed fittings. It is also difficult to keep the head plumb and level especially with rotor heads. Regular flexible PVC has a place in a light commercial setting, but it has the same issues with keeping the head plumb as funny pipe. I'm sure it has high pressure loss as well when running long lengths.
As far as installing an irrigation system using a shovel to make a slit in which to drop the pipe into, I don't think that you'd be able to get the pipe deep enough to avoid damage during aeration and other shallow excavations.
I wouldn't try to cut corners in this instance. You'll only be disappointed.

All Wet
Texas Licensed Irrigator #1897 since 1984

Thanks for the info.

How deep would you normally go with regular PVC?

I've never done aeration in the five years I've been here but it's nice to be able to in the future if necessary, in Texas we also don't get a lot of cold weather and I don't plan any excavations, but again since you are licensed maybe you can give me more info about depth options.

Also are there any reasons to use Flex PVC over regular PVC?

I thought somehow it would be easier, and maybe it is but it's also quite expensive compared to normal PVC, my yard is last on our budget so I'm looking to save however I can.

So far my shovel trench is four inches wide, and about eight inches deep, it wouldn't be too much work to make it deeper, I'm thinking of switching to regular PVC so any advice or direction would be great.

We ordinarily strive to get the main at a depth of 12", and laterals at an 8" depth. The law in the State of Texas states that all pipe be a minimum of 6".
We will occasionally use flex PVC in an area with some sort of obstacle such as shallow roots or other buried objects, but that is a very rare situation. One inherent problem with flexible PVC is it's best property...it's flexibility. Roots can intrude more easily into the flexible pipe. As well, the solvent welded glue joints are more fragile.
As I stated in my previous post, the pressure loss will be alot higher with flexible PVC because of the ID of the flexible PVC, therefore less GPM and fewer heads on a given run.
Stick with standard Cl. 200 PVC minimum which is the industry standard in Texas. Some will use Sch. 40 for the main, but it is not mandatory unless otherwise regulated by your local codes.

All Wet
Texas Licensed Irrigator #1897 since 1984

Go with schedule 40 for your entire system .. it's a much better product and the extra cost for a home is minimal. In my city class 200 pipe is never specified on irrigation mains.

Good Day ...

Why not Poly Pipe with Insert fittings and clamps?

Open trenching is way more work, and will scar your yard for YEARS.

Here it was schd 200 & schd 160 and I bought the 2 foot lengths of the black 3/4 schd 40 flex pvc that HomeDepot or Lowes sells ,, to hook up each of the heads. My swing joints if you will.

Yea the first season you spend some time straighening some heads. Yea when the roofers drive across your heads it sinks it into the ground and needs to be lifted up and straightened.

My yard I hand dug and shot for about 6 - 8 inches deep trenches which was mostly a piece of cake, unless oak roots needed axed, so I could tow around the core aerator every other month or so chopping up the oak feeder root thatchy mat. All things have been in since 99 and zero problems except for one hunter pgp that stuck after having the begeezus beat out of it with the core cutting it up one time too many & one pgp froze for no apparent reason - probably our florida beach sand one grain too many finally.