This is a product that I have been using since it hit the market. The standard Glock magazine release is small, low profile, and can be somewhat difficult to hit without really shifting your grip. Glock makes an extended magazine release that may be fine for competition but it is too large for a carry gun. I have seen it interfere with holsters or even cause the magazine to be dropped when the Glock was gripped aggressively or laid on a flat surface.
Larry Vickers recognized the need for functional Glock magazine release that was larger than the stock part but not so large that it causes more problems than it solves. The result is the Vickers Glock Extended Magazine Release which is made by Tango Down for Vickers Tactical. It is available for the 9mm/.40S&W/.357SIG/.45GAP sized frames and the .45ACP/10MM sized frames.
This release is perfect for a carry gun. It is long enough that it makes reaching the release much easier but no so long that it interferes with grip or holstering. All of the edges are nicely rounded which is nice considering how sharp some aftermarket magazine release can be. This is basically the only extended magazine release that I know of for Glocks that is suitable for carry.
This magazine release, along with a good set of sights, and maybe my favorite trigger set up is all that a Glock really needs.
Check out the Vickers Extended Mag Release For Glock at Brownells.