NoS1 - to be honest, the only advice I would give is to avoid this like the plague. They are reselling broadband access at (or very close to) the costs they are charged by BT just for the connection - and that's before usage is taken into account, which can cost a fair bit.
This industry is littered with companies that have tried to offer far too good a deal at far too low a price, and they all disappear sooner or later, often with lots of recriminations and customers being the ones to suffer the most.
To my mind there are 5 main types of ISP -
Ones that offer lots of bandwith and quality of service, but charge a price that reflects that - high compared to other ISPs, but you get what you pay for (Zen is highly thought of, for example)
Ones that offer low caps for a low price (great for people who just want pages to load faster than dial-up and free up the phone line, but no real interest in downloading). Last time I looked Namesco was pretty good for this - I used them in the past and they were excellent.
Then there is the ones that try to strike a balance between the two - not all are successful. Entanet resellers such as UKFSN spring to mind.
On top of these you have the big 4 (BT, AOL, Tiscali plus Virgin if you would consider cable bb). I wouldn't touch these with a bargepole - not even a very big one!
Then you have the niche market ISPs - I use Be, which offers 24mb with no limit that I've ever hit for £24 (there is a cheaper option with a cap - £14 for 4Gb at 24mb)
You choose your ISP based on your requirements, but don't go for the cheapest unless the price reflects the product they are offering.