Neoprene compresses at depth. At 100 feet, you'll have about 1/3 to 1/4 the insulation as you do at the surface.
Strictly as an insulation, neoprene is not ideal. You can get more warmth per unit loft with something like Thinsulate.. and when wearing nice warm undies you'll be as warm at 100 feet as you will at the surface.
Neoprene also leads to large buoyancy shifts as it compresses. Therefore, unlike air which can be vented from a trilam suit, you will gain buoyancy as you go higher that you can't vent. This is especially problematic in shallow depths where small changes in depth can lead to large changes in buoyancy. This is dynamic instability, where a small change in depth leads to a large change in buoyancy and results in a positive feedback loop. The more you go up, the faster you go up. This is of course alleviated by dumping your BC, but you have to be that much more on top of the air in the BC whereas air in a trilam suit is not only kept to an absolute minimum, but venting is virtually automatic. You have the manage a much larger air space (the bubbles in the neoprene) in a neoprene suit than a trilam.
The only reason to use a neoprene suit is that it's cheaper or warmer. Trilam suits these days are very inexpensive, and neoprene as an insulator is problematic and non-ideal. In other words, in choosing an insulation, neoprene should be far down the list.