I don't think you'll go far wrong with Bristol. I'm just about to finish the 2nd module with them; the CBT programme is well set out with regular testing as you go along, the manuals are easy to use (I just use them to supplement the computer programme, but I'm sure everyone has their own methods), friendly and knowledgable instructors on the brush-up.
The Bristol Q Bank is also IMO a useful tool, with the ability to assess yourself in each section of a subject and therefore easily identify weak areas.
One of the downsides I can see to Bristol is the fact that the exams are split between just 2 sittings which can be a lot of work. Its certainly manageable however, and I'm not sure of exact figures but the pass rate is fairly high despite this.
Location might be a factor for some people, who may find it cheaper to do the brush-ups closer to home; however if you're coming from Spain anyway, this more than likely not an issue.
If you want to know more about it, feel free to PM me and I'll do my best to help.