It appears the GT series is going to be available again soon. Don't have the release at hand to post. Something is probably on the Garmin site. Supposed to be something 'big' announced at the BM Classic too.
I agree with all that hays posted tho. Some others actually have both and say they see no difference - at least in the waters we are likely to be in depth-wise. Again, HB used it for years w/o an issue. Only when Low put out the vid that it got stinky.