Hi all. Still fairly new to this forum. I am transitioning back to SCUBA after freediving for past few years. I have a few freedivig suits by Elios and Marea. They are simply awesome. I have a 5mm unlined, smooth skin custom suit which I have used at Catalina in the coldest of months and was quite toasty. I use a 3mm Marea sharkskin with a mimetic pattern for use in Baja for waters in the 70s. Now, mind you, with freediving/spearfishing you generally burn more calories, but I can tell you these suits are fantastic. Very little water entry, great freedom of movement, and the unlined neoprene has amazing heat retention qualities.
I haven't used them for SCUBA yet here in California, but plan to experiment. The negatives for SCUBA would be, as mentioned, compression at depth. If I remember correctly,these suits are made of high-end Yamamoto 45 neoprene, or something very equivalent. Very spongy, but warm. SCUBA neoprene is denser. The other negative would be the difficulty of doning, especially in a multiple boat dive situation. I have to use a 50/50 solution of water and hair conditioner to slip into the suits or they will tear. When I first stating using them, I got my head stuck once for a bit while trying to pull the top down and over my head. Also, they are zipperless and have an integrated hood. The panels are glued - not stitched. The last negative is the durability. The smooth skin model catches on everything and tears easily, but boy do you feel streamlined in the water. I was thinking of using a rash guard over it for SCUBA to prevent tears from the bp harness. However, the Marea shark skin or exterior lined suits are very tough and I would not have much of a concern.
These manufacturers are extremely customer service oriented and the price of a custom suit is about the same as a mid-range SCUBA wetsuit off the rack. About $250 US, depending on what options you want - like knee pads or chest pad. Overall, these suits are excellent with respect to quality and very toasty. However, I can only imagine the looks I will get when donning a mimetic wetsuit on a SCUBA cattle boat to Catalina. But once in the water with these suits, you literally feel like a seal. So much warmer than my SCUBA wetsuits.
Check out eliossub and marea (made to measure) custom wetsuits on the net. I was not allowed to post their URLs.