I pretty much echo what @
fatdog says.
Concealability. I’m a pretty stout 6’0’’ and with an untucked shirt it doesn’t matter what I’m carrying AIWB. With a tucked in shirt, which is most days, there is a material difference between the G19 with grip anchor, and G45.
Shootability. There was a
big difference between G19 without grip anchor, and G45. With the grip anchor it’s about a draw. I might say the G45 has a slight edge due to the slightly longer handle, but it’s slight.
Switching between them? Perhaps a more sophisticated shooter than I would perceive differences. For me, six of one, half dozen of the other.
Concerns? With the grip anchor, you can’t use X-grip sleeves with 17-round mags. Otherwise, I maintain it’s the single greatest G19 accessory ever devised.