Done both in Monterey. Currently I'm diving with a 7mm neoprene dry suit. I like it more than my original (1980's DUI), easier to put on, and I'm not worried about small leaks. OTOH I don't dive deep. My guess is the insulation of the 7mm decreases with depth just like a wetsuit does.
I get cold easily. With an old style wetsuit (think 1970s or 1980s) 2 dives in a day were really pushing it. With a newer (very stretchy) wetsuit I can easily do 2 dives, but 3 is iffy. With the neoprene drysuit I haven't found a limit (4 so far).
As for training. I taught myself drysuits (remember late 70s, early 80s). I feel very comfortable with my skills. OTOH, I'm not letting my 18 yo son (deep away from AOW) from diving with his neoprene drysuit until he has a pool session with an instructor. I thought about this a lot before insisting. The most dangerous thing a drysuit diver can experience is an uncontrolled ascent. The most dangerous place for such an ascent is the last few feet before breaking the surface. The big danger is an AGE. You don't need to get drysuit certified unless you are trying to rent, but I would suggest a pool orientation session.
Lastly, I don't have any for sale, but do know where a large number of used drysuits (all types and conditions) is in the Gilroy area. Give me a PM if you want more info. It's where I bought mine and my son's. Very happy with both, and I didn't pay a fortune.