Unlike most of the comments above, I have several Glocks, one in particular in my pants and it does have a Saf-T-block in it.
No it doesn't get in the way or hinder using the pistol in any way. In fact ya can't draw and position your trigger finger without it popping out (once your used to it) and having it land on the ground or floor, as it's designed to do.
As I carry daily, it is quite comforting to know it's there, IMO. Here's a few reasons why I use it.
1. I'm an NRA licensed Instructor and SAFETY is a primary concern. I don't want folks seeing me toting a pistol like the Glock without some form of safety item, considering the way in which I carry it at times.
2. Should someone unfamilar or even familar with the G17, 19, 21, 30 somehow get a hold of one my pistols, unaware that it's there, it might actually hinder them in using the pistol, never a bad thing IMO.
3. Ya don't have to worry about "anything" snagging the trigger when carrying in an unorthodox manner as I do on occassion.
4. It dis-ables the ability to work the slide, futher confusing unauthorized use, even by those familar with Glocks.
5. It's MY pistol and as such works as I prefer it to, (see #2 & 4 above) even if it's strange or odd to some, getting shot with my own weapon IS NOT happening to me, if I can help it.
6. SAFETY is number one....., and although there are plenty of comments by those with strong opinions against them, MOST have never even tried one or they'd know this device sacifices nuthing at any point in it's use.
YMMV,
Mike