hmm, i'm not sure what you mean by tied to another account, but it's free money anyway and you don't have to play if you don't feel like it.
by bonus do you mean the starting capital? or a first deposit bonus?
the free $50 once given is already completely available to you for playing poker. i mean, you don't have to clear it in chunks in order to receive it in your account the way bonuses are. of course there are withdrawal requirements (you can't just receive it now and withdraw the whole thing immediately). but the requirements are very easy i think and doable on all the given platforms because you are really given plenty of time. even if you play on a different main site and just use the other one for fun (like on weekends or when you are drunk or trying to experiment with some crazy play or trying some different games like PLO or sngs if you play cash games) and it takes you 3 months to do it, it doesnt really matter does it?
the question of first deposit bonus is a different matter. on NL2, i really do not think it is very important to be honest. you should be focusing more on improving your play. i think you will quickly find that pokerstars has the best software out there, but also has the toughest field of opponents to win money from.