Okay, seriously. How did everyone miss the obvious here? The OP likes his friend's Dart and loves the feel of it too... So I'm thinking that MAYBE (just bear with me here), he should... Get a Dart. I know it's a revolutionary idea, but it just might work.
I'm an Ion user and am quite happy with them, but the best advice you'll get has been said on this thread several times now: Go with what feels right to you. And if the Dart feels right, then get a Dart. Or if the Teebird is working for you, keep using that and ask people out on the course if you can try their putters until you find something that feels great to you and flies great too. But in the meantime, just buy a Dart.
This message brought to you by someone who (ironically) doesn't like the Dart.