I would not worry too much about exhaust brake. There are plenty of folks pulling a TT and pushing the limits and drive it all over the mountains. The trick is to properly drive it downhill. So, if this unit does not have one, then just learn the proper technique on how to drive down hill.
Also, I would not be afraid to buy something that is old or high mileage. If it was maintain well, then you may have less issues. I just bought my truck and it has 160K miles and one owner. It was not maintained very well, but just enough that I trust it.
