IMO, no reason to put extention on a magazine made to hold 15 rounds, it causes more stress on the spring. If you want +2 get the Glock 17 magazine.
SHTF vs TEOTWAWKI you ask? SHTF, just some crap on the ceiling and walls, TEOTWAWKI end of the world as we know it. Orignally made by 9mm/®™©