Hi Chrismac,
AIM won't beat B&H in a market that goes straight up. However there is no market that goes straight up over the long term. So it's best to think of AIM as a long-term investing strategy.
Some people use it with a shorter time horizion in mind, but I've found that you need at least 5 years (on average) to really start seeing AIM work for you.
If you're interested in a shorter-term strategy, I'd recommend something other than AIM.
I hope that helps. Please feel free to post any other questions.