[parahandy]

Presumably when you say a FREE course you mean as opposed to paying for a course with PADI.

Understand where youre coming from when you say free, however I would guess that you will be expected to join and pay the Branch Annual fees.

Reading the posts on the other Newsgroups and Forums there seems to quite a lot of crossover to BSAC and SAA.
ADVANTAGES
1.If you join the BSAC Branch i'm led to believe youre covered by their liabilty insurance, presumably providing youre diving within their Guidelines.
2.If the branch has a boat youre likely to have access to this,usually but NOT always cheaper than using a commercial boat.
3.If you dive in UK waters a fair bit you'll find an excellent network of members and information on dive sites and local knowledge
4.A lot of BSAC branches have an excellent social side if you like the Club environment.
5.Courses run at a Regional level, O2 Admin,Chartwork and Navigation etc etc normally cheaper than PADI.

Most of the points above can refer equally to the SAA.