There are some pros and cons about being in BALPA but what I like is that they are a part of IFALPA (thats the INTERNATIONAL Federation of Airline Pilots).
Many years ago when Swissair went of the end of the runway at Athens and the pilots were put in gaol it was IFALPA that go them out NOT their employer!
When the proverbial hits the fan you need someone who is "batting" for you and in my opinion this is the best reason to be a member and the subscription is a small price to pay for the insurance they offer.