Isaeus, I'm sure you're aware but I figure it's good to add to the thread...
The
LG-617 fits both of those for anyone looking to put a laser on either the 20SF or 21SF GLOCK.
It's part of the G-Series so it does not have a master on/off switch, but it's a good low-priced option and it's easy to remove the batteries at the range for practicing without the laser.