Don't know specifically about TT. But Motoseries events are closer and offer good instructional groups. I'd recommend checking them out first and there's lots of members on here that go to their events so you could easily hook up with someone to take you and your bike for your first outing. EDIT: Didn't realize how close you are to PIRC. That is def. closer out of all the tracks.
That's cool, until you leave the cable or USB at home on a trip. I'm not saying the Nexus isn't good. They're all pretty much the same, really. I look for things that aren't limited by their design because I fucking hate Apple products.
I'm of the opinion that more money in my pocket means more track time. You're going to get something better than stock no matter what if you're going aftermarket. I say get the used one, have it serviced, slap it on and do more track days.