Not to be rude, but "doing fine but they weren't able to grow" sounds like PR bizspeak for "unable to sustain themselves". It isn't like Opera is a company that can really grow Fastmail when they haven't even done that with their browser. I don't see how you could particularly trust Fastmail to be around for an extended period when they were recently sold to company few would consider stable and healthy.

Then again, I don't really see the point of not using Fastmail as long as you can export your stuff.