The biggest downside to a GAP Glock is ammunition capacity. The G37 holds 10 rounds. The G17 in 9mm holds 17. In CA, you're prohibited from purchasing a weapon that holds more than 10 rounds, so you end up with a G17 with crippled 10-round magazines. IMO, the G37 makes a lot of sense in CA, assuming you can still order ammunition online.
Funny thing about Turner's Outdoorsman... About 2-3 years ago, they made the decision to not sell any "dead" calibers and had a close out sale on .45GAP, .357SIG and 10x25mm handguns. They also said they would never sell handguns in those calibers again. Look at them now. Selling a .45GAP pistol, but they're still not selling any .357SIG or 10x25mm handguns. Guess .45GAP isn't as dead as they thought.