I have a Sidearmor IWB for my G27. It's well designed, precision made, and comfortable to wear. Retention is good, but the gun is still easy to draw. After buying it, I traded away my other G27 holsters (ATA and Bianchi).
Sidearmor customer service is first-rate.
I might add that the Kydex holster material looks "right" with a Glock.