They're the same thing from the cockpit perspective. Historically an AH is a cockpit display only, but an AI also transmits data to other systems - in practice everything gets called an AI nowadays.
I also, incidentally, agree that a bit of instrument training + an AI are not a bad idea if you're doing long trips regularly in a microlight - equally the best lifesaver in a microlight is the ability and willingness to land in a field and walk.
G