Without knowing what you're towing, what you're towing with, and how far you are going it's hard to say whether you could scrape by at 40 mph without a WD hitch just to get home.
Assuming that you can't, ask the dealer if you can get the Equal-i-zer brand hitch. If he can get the E2, he should be able to get the Equal-i-zer, since made by the same company. Could be that those two options are the ones he is willing to "include" in the sales package with the trailer, ask if he has other hitches available if you want to upgrade. If not, ask if he will install a hitch if you buy it and bring it with you.
Worst case, it's not the end of the world, pick one of the two he is offering and tow your trailer home. If you don't like it you can always sell it on CL and upgrade.
Regarding installation, please take some time to read and digest this
sticky at the top of the Towing Forum regarding WD hitch set-up.Your dealer will install and adjust the hitch before you leave the lot, but it will need to be adjusted again. The reason being once you pack all your stuff in the trailer, how/where things get loaded will affect the weight and balance of the trailer and 99% of the time the hitch will need to be re-adjusted. Also where the water tank is located (ahead or behind the axles) and whether you plan to tow with water on board.
Once you have the trailer home and packed the way it would be when you go camping, follow the procedures in the sticky above to get the hitch dialed in. Don't forget about cargo in the tow vehicle, that will affect hitch adjustment also.
First TT in 2000 I got the standard hitch from the dealer and let them install it. I thought I was smarter in 2002, and on our 34' TT I told the dealer to keep his hitch as my brand new Hensley was home in a box. Drove home about 20 miles with a borrowed hitch without WD, the trailer would start to sway if I got over 45 mph. Headlights scanning the trees ahead for squirrels. Was not pleasant on the expressway at rush hour. Current TT I took the Hensley with me and the dealer agreed to let me install it myself in the parking lot. Of course it was December and it started to snow....