Anybody here use a Smartcarry Holster? If so, what do you think of it? Do you always have a fear in the back of your mind, that the gun might go off and hit yourself while sitting down?

I use one carrying a G19 or a G26. I like it better than my C-Tac. All my packing is in hot weather.You cannot make a Glock discharge while it's in the holster.Before i started useing it I tried real hard to make it go off but couldn't. HTH,Nick

Do a search and you'll find several posts on this type of carry.
I wore mine at work today with an SP101 in it.

The one thing I really dislike is the wide velcro on the straps.
The corners are sharp, the undershirt I wear between the straps and my skin, sometimes gets caught by the velcro.

I may come up with a different fastening method for mine soon.

I have NEVER worried about my firearm 'going off'.  I have no worries about shooting myself either.
I practice with everything I carry.  I use a redgun for some of the practice and the real gun unloaded for the rest of my practice times.
I'm confident I will not have the gun go off until I am clear of my body.

Yep, got one on as I type this. SP101 with a Hogue grip and speed loader. Ususally don't even give it a second thought. I would suggest an undershirt as it makes it much more comfortable to wear.

You're probably thinking that the material might bunch up and get caught in the trigger guard, and possible make the gun go off.  Some such possibility seems so remote to me as to not even consider it.  It's good that you're looking ahead, though.  I have one and very much like the concept for a G26 or snubby.  I agree with the other post which says that the velcro chafes a bit.  Also, you'd be hardpressed to re-holster in a hurry.  But that's true with nearly all concealed holsters.

I carried a full size 1911 in a Smartcarry and I really liked it.
No problems. No worries about it going off.

I use a Thunderwear occasionally with a Glock and have never worried about it going off.  I wouldn't want to carry like that every day, but it serves it's purpose.