You can't do anything else in that time. "No interruption" sounds OP but you can't cast any spell since you're already casting town portal. And it's not an immunity bubble, it's just 50% reduced damage. But in that time of standing there, your opponents can unleash hell on you. Not sure why you think this is gonna be super OP in PvP. If you stack crazy health regen maybe, but then again - if you're regenerating more than what's half of your opponent's unhindered damage, you're OP without that bubble, too.
i dont think you can even tp in pvp, yes you can do it in brawling, but when the real pvp hits, it will be most likely like deathmatch/team deathmatch
I was about to say this same thing...
Sure, a person can Town Portal during Brawling, but Brawling is really just practice for what real PvP will end up being, as well as a way for the devs to test how balanced or imbalanced players directly attacking each other would be, to see what they would have to do to the game, as well as actual PvP environments, to make player battles more reasonable.
So yeah, I wouldn't worry about that one being OP in PvP. Seems like a great item for Hardcore, though. Not as easy to exploit as instant TP escapes in D2, but at least enough of a buffer that you can escape a bit easier.