Now this is not first hand experience, but from what I have read the t-5's are suppose to be brighter than traditional VHO bulbs, and use half the power. This still does not mean that they are up to the same standards as MH bulbs. 1 disadvantage to them is that they do not have the reflector built into the bulb like the URI VHO's so you need a reflector for each bulb if possible. By the time you add that, the bulbs are not smaller than a VHO, though they still require less electric to run. I expect them to be a lot cooler as well, but That is mroe or less a guess. I just ordered a pr of them, to go with a pr of vho antics. I hear that is a pretty good conbination.
http://www.aquaencounter.com/ has some good info about the lighting itself.
Once apon a time I saw a link for individual reflectors for these bulbs but, I guess I forgot to bookmark it.
Edit: I think the reflectors are at :
http://www.aqualuxlighting.com/reflectors.html Thanks Probuilder.
HTH