I don't have a Frontier here to compare to (did have a Mini size pony cart many years ago & Mom says it was a Frontier) but I do have a CTM. I've had it over a year now and have no complaints--I am very happy with it. I've compared the specs & it's pretty much the same in size so I'm quite sure there is little difference in leg room/seat size/overall comfort. Durability would be the only difference, and I cannot say if there is any or much difference in that department. Like I said, I sure have had no complaints about mine. There is another EE cart sold here in Canada that more than one person has told me they bought, used it once & hit a bump or horse jumped/spooked & the cart fell apart--and I'm happy to say that the CTM is nothing like that not-so-cheap variety!!
I had a couple reasons for buying a CTM instead of a Frontier. First, the purchase price was lower on the CTM. Second, with the CTM a friend was able to pick it up from Ozark Mtn. and bring it home for me--and so, no shipping charges for me. Frontier would have meant a sizeable shipping bill plus I'd have had to pay the outrageous UPS broker charges to get it brought up across the border. So, overall cost and convenience made my decision, and I'm happy with what I got.