I'm half way through studying the second module with BGS. I had the same fears as you did before I started studying - don't let it put you off. The course isn't THAT hard (although it's certainly not easy). I found that BGS' notes and CD provide more than enough info to adequately explain everything, and so far, I haven't needed to contact anybody to ask for further help. However, If I needed to, Bristol make instructors available for you to contact by phone, e-mail etc, and from the instructors I met at the module one brush up course, they certainly know their stuff. You've also got this forum to ask other questions if you don't feel like contacting the school directly.
Remember that as it's distance learning, you can study as quickly or as slowly as you want to - there's no real pressure!
I've also found that studying purely on my own means that I have to use my own brain to work things out, and therefore I understand them in more depth. The hardest thing I find with the course is purely remembering the huge amount of information needed for the exams.
Good luck with whatever you decide to do!