Full of very questionable companies from little I know about it. AIM is meant to be a stepping stone to bigger exchanges I think, but it's full of VERY illiquid stocks and dodgy directors. Also spreads are ridiculously high.
Look at this one I bought years ago (I know, lol @ me)
http://www.londonstockexchange.com/e...CDXQ41GBGBXAIM
Bid 0.5, ask 0.6, ~17% spread
Because they are so illiquid and low cap they are susceptible to dodgy goings on. That why I would never invest in a micro cap like this again, there's a lot more security in larger caps where individuals can't influence them so easily.