ADSL24 is a company. ADSL2+ is a technology
I've just had my FTTC install done for Zen. The engineer was quite surprised at the stability of the download I had - he thought it may be something to do with being on Zen instead of BT.
I know it's more, but it's still cheaper than ADSL was when it first launched - and experience tells me that it's just not worth going for the cheap ISPs.