Which makes them perfect for today's and tomorrow's computers - use SSDs as main drives and HDDs for data storage. But I think the write speed will be good enough to use these drives as main drives, as well...

As for reliability - I don't think it's going to be that much of an issue - I've had CD-RWs that I used as portable storage and wrote/erased/read dozens of times (with scratches on them from constant use). A fixed platter in a clean housing should last quite a while...