> 'Import' is as easy to use as Graft and as far as I know, the result 
> when successful is the same.

I use import while importing patches from the tracker, but once I committed on 2.x it's easier to just graft instead of importing again (importing often requires you to generate a new patch and possibly you have to commit manually again after the import).

> I know I 'should' learn to use kdiff3 effectively, but it seldom works
> right for me,

That's what learning it is supposed to avoid :)

> and the live repository is the wrong place to learn by failure.

As long as you check the result before pushing there shouldn't be any problems.  If the merge goes wrong you can always rollback and try again (or try a different approach).  You can also use "hg diff -c tip" to see the diff of the last commit.