I use Mega regularly and while I do not trust their security too much I still view them as a provider worth considering primarily due to the 50 GB free space on offer. Suggest you encrypt your data and then backup to Mega. I use Duplicati for this purpose.
The only point of using mega.nz is that they're not too regarding on copyright. And that's a plus even if you use 100% legal data. For example, I've read some cloud service scans your library for copyrighted content. That might be a problem if you have a collection of MP3 that you ripped from your owned CDs or converter from your iTunes purchases, for example.
It's also a good for less important stuff. But otherwise i wouldn't trust them with my real personal files, as this provider is often associated with pirated content.
And if you're going to go thru the hassle of encrypting your files, why not encrypting your files on safer cloud service ? Then you'd have more security