We need to write one of these. Anyways, this is a version for Shotokan karate. This guy is pretty hard edge in a lot of ways but in general I think he did a good job with this part.
Personally, I don't think you can accurately judge a fit for at least a few months and even then it can be hard to be sure as you and they change. Dojos go in cycles. They can be very martial one month and the domain of lovey-dovey flower-sniffing foo-foo fighting skirt wearers the next. It's almost impossible to tell out of the gate as not only don't you know them, you probably don't even know what you really want out of the art.
You are going to have to make the best decision you can and jump in--after going to as many dojos as you can to watch several classes. Use your common-sense, intuition and judgement and go for it. You can always get out of the water and go jump in a different pool if it doesn't work out.