I've just completed module 2 at Bristol, and have just my Air Law exam to do, which is tomorrow!
Bristol are excellent, it's an intense two weeks but gives you a good grounding to sit the exams. From my experience going through the distance learning material will give you about 75% of what is needed for the exams, the 2 week brush up course sorts the rest out (loads of 'lightbulb' moments over the 2 weeks!)
In terms of time scale, it depends entirely on circumstances as to how long it will take you to complete the course. It's taken me about a year to do all 14 exams, but I work full time so can only study in what spare time I have. There were people on the same course as me who had done in 6 months and in some cases less, just depends how much time you can put in.
The question bank is brilliant, and is virtually identical to the questions you will get in the exam, however you can't get by just learning the questions (particularly for principles of flight), the CAA occasionally change numbers on some questions so that the answer is different. There are the odd exam questions which are genuine rubbish, but Bristol will point these out.
Where do you plan to sit your exams?