I've just started doing some instructing on 3-axis microlights (C42s). I was checked out by the schools CFI for 2 hours and then got a 'differences' sign off in my logbook. The checkout was mostly to show me the differences required in flying technique between the C42, and things like the 152 and Warrior which I was more used to. A lot of emphasis was placed on the low inertia the microlights have.
I have to say I'm still feeling my way around the rules and regulations regarding these aircraft. The JARs pretty much seem to regard them as coming under national regulation.