While MV lamps can be used for growing, they should be avoided, for a few reasons that I know of.
1) They use a lot of electricity and produce a little light. They are not very eccicient. So if they use the same amount of electricity but put out less light, that means that they are generating much more heat. These lamps get very hot, which makes venting even more important then with HPS's or MH's
2) Even the improved spectrum one, put out a crappy light spectrum. While you can use them, your plant can not use the majority of the light spectrum.
So just with these two points, I would say if it can be avoided, then avoid it. With it putting out half of the light of an HPS and then half the output being unusable, it will not be much better then using flouros as for the light produced, and will get 10 times hotter then a flouro.
But these are just my opinion from the research that I have done. I have never used a MV before, but these are the reasons why. You could always try it, and please wait for a second opinion because maybe someone is or has used one, I am only talking from the research I have done on the topic.
I hope this help you out some.
Peace
MassProducer