depends on if you look at the fail rate on things now days. Things are NOT made to last like they used to be. They're made to be thrown away in a year or two. Why do you think its cheaper to replace something when it breaks then repair it?
Id still rent the modem over buying it in terms of fail rate and the ISP HAS to support it ad not give the BS of "sorry but we can see you and that's all we can do unless you use our modem".