Any idea how far you are from the towers? If not, www.antennaweb.org
will tell you. There have been mixed results on that antenna they give you. I dont know much about it except what people say on here. I'm 40 miles away and had to buy a bigger antenna to put on the roof. If you are close (10 to maybe 20 miles) and have a great line of site, maybe the DTV one will work.
I'd make sure you try it out before you sign paperwork. If he can't get it working to your satisfaction, dont sign, make him take it back and get your money back. A lot really depends on your topography and distance so no one can make recommendations until we hear what they are.
Also my guess is he will use a diplexor at the dish and then at the HDtivo so he doensn't have to run a separate antenna wire. That can be a problem too. That's why you need to check every channel you want before he goes in order to minimize problems.