fwjc, don't know if you have any connection with CATS PPL Groundschool, but as an embittered old cynic who also happens to work in the ISP industry I was put off by:
1. The fact that their registration form is hosted on a completely separate domain (
https://secure.sworddrawn.net) from the main site
2. They appear to require an inordinate amount of personal information, including my passport number which they say is mandatory
3. There being apparently no validation on their registration form - you can leave all fields blank and click submit and you get a cheery message thanking you for registering
Item #3 suggests a lack of attention to detail which would seem to preclude any possibility that item #2 is likely to be handled securely.
I'd suggest that sticking to the books already mentioned might be a better bet.