I've tried it in the past. Never works for me. Regardless of the server. Once I've been put in a team in the first round, for some reason it's impossible for me to switch even when I go to spec or it's another round. Works as it should as far as I can see.
you can easily abuse the system , especially in siege , but battle works well , the key is not be part of the balance by going spec , and as soon as its balance arrive choose a team ,
In siege you can offense 100% of the time with the trick or close to , in battle its trickier but you can even out the balance by going spec if you got a good kdr , they will put a good player in your team ,
Thats how it work and how easily it can be fooled , one fix would be to remove team choice and put SINGLE LOGON like it was eons ago in CRPG
edit : please all , abuse the mechanics it will force devs to rethink the balance system