safety glass is different from toughened glass, safety glass has a plastic sheet in the middle so is no good for heat but wont break, toughened is heat treated, its hard to break but when it does goes into a million pieces.
I also think the chances of the outer shield glass on a single ended bulb breaking and falling off enough to stop it blocking the UV and the actual bulb still working is slim, but I could be wrong.
Anyway the point I was making in my first post is the glass will still smash if splashed, and it makes a real mess. Its probably 4 months since I broke my glass and I still find bits of it in my tank every week. The other down side is the extra salt spray you will get on it blocking the light since it is closer to the water level, but I guess its easier to clean off.