Beautiful, but not cheap. I was considering this ages ago and emailed to ask if it was poss to buy it and later on if need be use a 150W bulb. They said that this is not poss and I would need to buy a whole new unit.
I reckon if you get a 150W one, you better fill that tank right up with plants otherwise you might have problems!
I'd love a MH, but I think that they aren't so great on smaller tanks.
EDIT: Just get a 24W T5 Osram 8000K for a fiver, the difference is worth the money tenfold!