Big, big difference is the fact that a regular loan you start paying it back straight away, with the CDL you only start paying it back one/two month after your course has ended. This is because it is a 'deferred repayment' loan.
The Learning Skills Council pays the interest on it whilst you are studying (and for the month or two afterwards). So basically you don't have to worry about the loan whilst you are no your course.
The bank offers you a choice of interest rates depending on the length of the term you choose.
I got a CDL last October from Barclays for my Masters course. I won't start paying it back til Oct/Nov this year. I personally found it was very easy and quick to apply for.
Find out more from www.direct.gov.uk/cdl, there is a link on the site so that you can get a free phone call from an CDL Advisor who will answer any questions you have.