I tried it for a time and it was slow and riddled with bugs. These included generating replication conflict errors in cases where such errors could not have occurred in the first place if there hadn't been bugs in the software. As a result, it was liable to delete both the cloud copy and the original
of some documents; especially Microsoft Office documents because of the way they use file locking.
I think most of the bugs have been smoothed out and the speed improved, but I would never have felt comfortable with it.
Dropbox, Google Drive and Microsoft Drive (or whatever they call it this week) prices have dropped abruptly too since I tried BT Cloud. For most people the 50GB free is not quite right. If you only want to keep documents you will probably get enough free space from Dropbox, Google or Microsoft. If you want to store photos and videos you will probably find 50GB isn't enough.
Recently moved from BT Infinity 2 to PlusNet. Very happy so far.