The H&K showed up late, so here are the other three side by side.

The standard sights compared Glock on the left and below the XD45 on the right of the picture to the left

The G21SF and the G19 head to head

The G21 is not  too much larger than the standard large size Glock frame

The Glock 21SF weighs 1 pound 3.4 ounces while the Glock 17 weighs 1 pound 8.8 ounces

The XD45 5" Tctical weighs 2 pounds 0.2 ounces while the H&K USP 45 weighs 1 pound 15.2 ounces

The Glock 21SF and the H&K USP 45 side by side

The Glock 21SF and the H&K USP 45 are close to the same size. The new Glock has a standard light rail