Hi All, I've been out of the Glock world for about ten years. Went back to 1911, discovered the great BHP and SIGs. Recently I pulled out my old Gen 2 19, Gen 3, 26 & 34 and had a ball. So it's time to get back into Glocks. I'm looking at a 21 with what i guess is sf (short frame??) and of course gen 4 is completely new to me. Are the Gen 4 21 sf good pistols? Anything I should be aware of...problems with gen 4 etc.? I looked at gun brokers and best price was around $575.00...Ok price? Sorry for all the question but I'd like to get it right the first time. Thanks in advance for any help you all can provide.