Hello,
The velcro one blows donkey. After a few pieces of brass get in it, it starts to twist.
The 3Buuc is the best. the one for a carry handle attaches under the handle, and has a pin at front and back that goes into the mounted adapter on the handle.
The one for a flat top, has a little piece with two holes that you mount on the front of the rail (so in front of your scope), the two prongs on the catcher goes into this adapter.
Both bags allow to be opened from the bottom, so they can be emptied without removal.
I have both kinds and they both work well.