I'm just coming to the end of mine right now with Bristol.gs. Got my Mod 2 exams in December.
In terms of work load, it is definately 'doable'. I worked full time and it has taken me just over 11 months.
It depends on your character more than anything else. Some people can work 4 hours EVERY night after work. Others prefer to do it full time knowing that they will not have the motivation to do both. Others just want to 'get it done' ASAP.
Believe me, it does get tough in terms of the amount you have to cover (not the actual content though) if you are working full time. I just thought of the money I was earning compared to those who were not working. I'm about 11K better off!
BTW, BGS are excellent. Highly recommended.
EK