I'm using a velcro belt with an MTAC holster and a Glock 26. I honestly can't tell a difference in function or feel compared to when I was using the 'C' clips. Well, that's not quite true. The velcro setup is a little more comfortable due to the clips being shorter in length, I think.
In both cases I got the belt nice and snug. Velcro really doesn't like to move when you apply shear to it (as opposed to pulling it away).
One thing I would change. I got a 1-1/4" belt rather than a 1-1/2" belt and I wish I had gotten the thicker belt because the portion of the clips with the velcro is actually wider than my 1-1/4" belt and it peeks either above the belt or below it.