I shoot a g-27 in the back up gun class in IDPA , works ok , i use the same extension i think GB uses , makes a 27 feel like a 23 as far as grip ! I have not found it to shoot as accurate as a 23 !
Never much got the point of extenders. I have several mags for my subcompacts with them, but have found them pointless.
Point being, most of us want subcompacts for concealed carry. Usually, the longer the grip, the harder to conceal. Slide length is usually not an issue, especially if you use an inside the waist holster.
So why get a subcompact, put on an extender, thus making the grip basically as big as a compact's grip, but still have the shorter slide... giving you a shorter sight radius... and a shorter barrel... giving you less (but negligable) velocity?
Why not just get a compact?