For what its worth I think I'd only consider 3 axis micro's. The main reason being purely that they are the closest to 'real' enclosed aircraft as you can get. A flex wing, in my un-learned opinion, is purely a hanglider with a engine.
Anyway after all of this I dropped off at Oxford airport today and was oh so very nearly persuaded by a skillful salesman/instructor to forget microlighting and pay to finish off the PPL in a PA28. Oh so tempting.
Yours,
Confused, of Oxford.