I have never had a problem with function, but mostly this was for look cool value in the photo. When I was in the CF my unit and me were investigated by the military police because the unit came up severly short on thermolds during an annual tech inspection. They thought people were stealing them. That is until I showed them the CRATE of mags that were nonfunctional. Either cracked down the front, or the baseplate retaining piece was broken off when troops tried to take apart the mags to clean them (not suggested). I have never seen one melt with ball. They did have various problems with blanks and a bfa. All had to be cut on the front lip of the mag as the crimp on the blank would catch on it. They eventially went to a longer crip on the IVI blanks which rectified the problem. They have also been known to melt with abusive full auto fire with blanks. Ammo discipline with live ammo does not allow the average troop to shoot mag dump after mag dump, but I would assume the problem would be the same with live ammo.
The CF went to standard GI spec US mags. While I was in, they only issued the US mags to operational troops but they have completely transitioned.
Now that I am an armchair commando, the mags work fine as they are not abused and I know better than to take one apart.
A fix if you do break the base plate retaining clip is just to hold the baseplate on while you melt weld it to the mag body with a cigarrette lighter.
I believe they are substandard for GI use. The follwer is very easy to tilt as well. Not worth the money when you can get GI mags for the same price.