I see you didn't follow the wheel treads, that have been here for years. In short:
- magnesium is lighter than aluminium, but it has a habbit of getting weaker by time if corrosive environment is there. Like air. So they need to be painted very good. Most magnesium isn't road legal because of that. Or not guaranteed to last long.
- Most PVM wheels are now forged alu, forging makes material stronger, and so with less material you have same strenght. They even have forged magnesium.
- Marvic does offer forged wheels too, but not in the piuma series.
PVM was a good german supplier, but now it seems they have lost interest in selling wheels a bit, because they have big orders from a bavarian motorcycle company.
Marvic is italian, and seems to deliver like you expect from italians.
Looks like PVM is slightly more expensive, but well you have to campare the same product to be fair.
Shipping from somewhere in europe should be roughly the same.