I would love to go with them! But sadly I live in a rural area that barely gets 3mbps from the major companies so I doubt an independent would be able to get even that :-(
A&A uses lines from BT Openreach and TalkTalk Wholesale. They're great at getting the most from a line - if you're getting 3mbps from a major, you're likely to get as good or better with A&A.
By not accepting poor performance from their suppliers, and by taking advantage of the control available for things like the SNR margin:
http://aaisp.net.uk/broadband-trial.html