Yes, I am using it for three months now.
I had the same concerns at first, I was using it with a sling; just in case. The only way that the camera could fall off is if the metal clip on the belt breaks in two.
The belt got a padding section that prevents the camera from hitting your lap on long walks; so you dont feel it. And the holster itself is fixed on the belt and you have two screws securing it through the belt. I compared this to a real Spider belt and they're identical; except for the price and logo.
You have a mounting plate that goes at the bottom of your camera and the screw is very solid when tightened enough,. It doesnt get loose or anything. Same kind of fixture then on a black rapid sling. On the bottom of this plate, you have a duplicated mount where you could put your QR adapter; whatever model it is. I'm currently using it with my manfrotto QR and works ok.
Ok, I wouldnt use it with a bigger lens then my 70-200; but with all the other ones I have, there's no stress at all on the belt.
And you have a locking pin that prevents the camera from going out of the holster without having your finger on the pin; so yes; very secure.
The belt has a locking mecanism too so you cant open the plastic clips to remove the belt if this mecanism is at the locked position.
I cant post a pic when I get home, but if you check online, its IDENTICAL to the Spider holster.