I was a member of both BALPA and the IPA at one point. I dropped my IPA membership as I felt they rather duplicated each other, and decided that as my company recogises BALPA it wa for me to play the white man, and subscribe to the body that represents my interests to the company, or at least , is supposed to.
The IPA provided a much better employment service, and much better advice than BALPA ever has. Any time I had a query for the IPA it was dealt with if not there and then, by a return phone call. I have never experienced any such level of service from BALPA. It is always so complicated to do things such as to update data base entries with the employment service, or to get any decent information as to how I might develop my career, or about who pays how much and what their terms and conditions are like etc.
I am currently reviewing whether I will change my alegience. If I leave BALPA I will still benefit from any change in T&Cs negotiated with the employers, without the 1% salary penalty that many of my collegues at work do not incur.