I used the Pearce +0 extensions on my Glock 27. They worked well but I feel it printed more under a T-shirt. It got me thinking I might as well have a Glock 19 or 23.
I bought a Glock 19 and, for now, I am back to the flat stock magazine setup.
If you get the Glock brand extension, also get the magazine insert. I don't know why they are sold separately.