I wouldn't judge a club on that necessarily. I mean, a lot of clubs are mostly GSDs. Schutzhund was actually developed as a temperament test for GSDs
This club around here is pretty serious about the sport and have mostly GSDs, a few Mals, a few Rotties and I think a couple American Bulldogs. This club has a great reputation and their helper is well respected. They were
extremely welcoming to people interested in the sport and accepted all breeds. I remember a couple brought a very soft BC mix and the helper actually laid on the ground to try to get the dog to tug with him.
A club who says they're all about fun is fine...as long as they are knowledgeable. You really need a knowledge helper, even if you're just doing it for fun. Most things actually end up being more fun to participate in if the people you are working with are knowledgeable about the sport. Not to mention safer. A police dog in my area broke his neck during protection practice when he wasn't caught properly
That isn't to say people in the club you mention aren't knowledgeable - I have no idea if they are or not obviously
If they are knowledgeable, welcome all breeds and people who just want to dabble in the sport as well as those who want to compete then they might be a great fit for you. Although be warned, it is a hard sport to just dabble in LOL