I was thinking of getting a S&W M&P 9 or a G17 and then I shot a 21SF with the picatinny rail and ambi mag release. I loved it and have a few questions. 1. Is it available with the Glock rail instead of the picatinny rail? 2. Are there any problems with the ambi-mag release? 3. I thought that I read there were problems with the internals rubbing or binding up? 4. Is it worth waiting for the 4th generation G21 to have the newest generation or will the 4th gen basically all be SF's with the adjustable backstraps? I would love any and all feedback with these questions and any other problems or advantages to this Glock!