im in an IRTA now in phoenix and as far as a "thing to do in a year off before med school" type job it is pretty nice. the pay isnt so hot but the health benefits are badass. ive heard from IRTAs in bethesda that they are worked really hard. im not, my lab is kind of wierd and not that high pressure, but others certainly are. the good news is the experience has come up in all of my interviews and they seemed universally impressed wiht what i was doing, what i had to say about it. my spot was pretty easy to get, i got several emails from other pi's that sounded neat. if you want one youll get one, thats how i understand it.
i would advise you to search labs you are interested in working with and email them to see if they need an IRTA. i got contacted form several labs but emailed the one i wanted and they took me, so dont wiat for a particular PI to get in contact with you. make sure to try and get some contact info, get in touch with a past IRTA to see if they liked it, if the lab totally sucks or if they were worked to the bone, and go visit. they dont all require an interview but its good to see the place. also the paperwork took forever so do this well in advance, it took around 6 weeks after my lab accepted me for my paperwork to go through at bethesda and for me to start