Do they only do backups or also cloud storage? If they have an API for uploading / deleting / viewing files, I'd use them over S3 given how lower their costs are. But, I can't find any info on that on their website.
To expand on this, we require our client because of our pricing model, which is $5 per computer for unlimited storage FOR THAT ONE laptop or desktop. An API would mess with that pricing model, so we haven't opened it up yet.