The guys over at ar15.com seem to think pretty highly of them.
They are similar to the steel magazines manufactured by Imperial
Defence Industries of England, and I believe they are intended for
the SA-80. I have two of the IDI magazines--they're much more
durable than the aluminium USGI ones, but I had to file away about
1/32" of metal from the top of the latch
engagement hole in order to make them lock into the magwell.
As a bonus, the IDI mags already come with the upgraded "anti-tilt"
followers.
MG