The company only have to negotiate with the recognised union - Balpa. All the rest can do what they like but they will never have a say if and until they outnumber and get formal recognition.
If your contract is issued in the UK, you should join the UK Union. If the situation were the other way round I would certainly join the national union of my contract issuer. Until the rules/laws change - that's the way it is folks.
At the moment, a German (for example) working for EZ is wasting money payng for membership of VC. If the guy found himself in difficulties VC would not have the right to represent him, and Balpa - under the IFALPA banner - could only provide emergency cover.
NSF
1% is par for the course for professional body membership (doctors, lawyers, EU pilot trade unions etc). Don't forget tax relief applies now in the same way as it does to other professional bodies. Also the first 2 years are cheaper, it's free for cadets etc etc.
TG may well be cheaper but it cannot provide the sort of specialist help that might sadly be needed one day. I've already seen it too may times that TG will drop a case without much of a fight. If I ever get into a jam (whether my fault or not) I want someone to fight my case until I say stop or I lose - that's what I pay for.
United indeed we must stand!