For the cost it’s fine I suppose, but I doubt you have LUKS encryption or such which makes you use ownCloud’s encryption.
Well true, though you can do an LVM volume with its own LUKS encryption for each ownCloud you host or even for each user, it’s a hassle. I chose to keep the ownCloud encryption, it’s more stable now even though I’m still a bit concerned sometimes about its behavior. The PHP overhead is now lesser but true that it used to be one huge pain in the *ss. Careful about the storage of the master key, if you can don’t host them on the same machine you have the data, if someone steals the disk he could access all the data ! It also seems the master key is stored in the database, but yet I sadly don’t know more about it.
Yep it’s one important point that can’t be put away 
I don’t know this service at all yet, I doubt you can have encrypted disk with it though. I’d suggest to send only encrypted files there, well it’s a basic rule
to me for any cloud solution anyway.