Its unlimited what you download, not speed, VM uses Vodafone and their speeds are capped, and if you live outside a city then you will get even more terrible speeds, I think the best you can get from Vodafone, this is from their site, is about 60Mbps down and 23Mbps up (in my area, if I am very lucky), their coverage is crap compared to the top 4, they are not the best outside big cities, must of been a very cheap deal they made with VM, I would not force it on my customers if I was running VM that's for sure.
Regards
(VM Mobile with Vodafone is pants outside cities)