Know nothing about? I have shot one. I have held the Glock 37. I also have held the XD in 45ACP and it is plain that the solution never was the 45GAP but a frame-redesign and getting rid of the polymer magazine shell - if there ever were a solution needed. And, if you note, there is at least one agency that has re-thought their choice of chambering.
In any case, Glock is almost giving away the 37's. The predicted wave of adoption never happened, even if some agencies adopted it.
As I have mentioned, the 45GAP had to deal with the end-user. The 45GAP user is a rare fellow, somebody with small hands who is convinced that 9mm is unsuitable. Since we know that modern 9mm ammo is certainly capable of doing what needs to be done, 9mm guys have no reason to drop number of rounds. Ditto for 40S&W. So, 45GAP, by design, must target that user who has no confidence in 9mm or 40S&W, but has hands too small for 45ACP. Talk about a niche. And even then, careful design of the pistol would have prevented Glock 45 pistols from being utter bricks in the hand - as the XD proved.
Ash