There is some weirdness, however -- about 30% of the time, clients are not receiving the Download link in their email, so I have to manually send them the link. This is quite a pain. They've checked their Junk Mail folders, too, and it isn't there.
By main gripe, though, is the support provided by Ossolution. Other people's experiences might be different to mine, but I have requested support from Ossolution on two separate occasions, for two different reasons. BOTH times I had to wait weeks for any kind of response. Given that this is a commercial product, and given that it's an extension aimed at raising revenue for your site, this isn't up to scratch -- twice I lost quite a bit of income while I waited for any kind of reply. (The reply, when it did arrive, was helpful and did solve my problem... but it wasn't anything dramatically complicated and could've been attended to fairly quickly.)
On the other hand, I know others who've been very satisfied with Ossolution's support. But I thought it was worth mentioning my own experience.