Have you tried SmartGit 8 preview?

So you want a way to copy the tag message?

Our intention was to keep it as simple as possible and though providing some useful functionality.

IMHO technically impossible.

Are you referring to SmartGit 7.1 or 8? Yes, there is a reason why not all Hg versions are supported: there are incompatible changes in Hg, so required SmartGit extensions have to be version-specific.