On what? I think with most pistols it's bad for the extractor.
The Mythbusters always do it when they're firing from that fixed pistol vice thing (ransom rest?), so I wouldn't think it's 'unsafe'.

It's not "unsafe" but most people will advise against it as it puts unnecessary tension on the extractor and can cause it to wear. The Beretta 92 series is an exception to the rule as far as I know though, and they consider loading it by the breech an extra feature. I wouldn't do it on anything though, including Berettas.

Also, k9870, what's wrong with your Taurus?

cylinder won't lock up and comes open when firing.

used the tis quick cuff today it is awesome

Shot a buddys cw40 today, twice the mag dropped most of the way out and we only shot bout 40 rounds. Also my hand flt good the recoils not bad at all but my trigger finger got beat up, it was weird.