I have an AR with a chunky aluminum rail height gas block. It it were steel, it would be half a pound probably. With the very moderate use I've given it, no issues. Being somewhat concerned about it in the back of my mind, I noticed a similar thread a while ago, where one or two guys confirmed that they had the same gas block and each bump fired or mag dumped at least 2 or 3 magazines multiple times with no issues.
Thats good enough for me for a range rifle. For a SHTF rifle, I would still get a steel gas block even it was over kill, just because. Some well known companies put tons of aluminum gas blocks on their rifles, which they would probably not do if they routinely failed under normal use.