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.
I don't have a CTM cart but do have a Frontier EE cart for the minis, and I used to have one for my biggies when I drove him. I love the Frontier EE carts. I have another metal EE cart that I'm not as crazy about. Then I have a wooden EE one which is actually my favorite of my EE carts. It is heavier than the Frontier cart, but it is more comfortable and I think very pretty (I love my Houghton show cart, but I would not be "ashamed" to show with this wooden one). It came from Mini Express and was about $500 (comparably priced to the Frontier when I bought it yeas ago).
PS it's been an age since I bought my Frontier -- 2001, I think. But the shipping was around $50. I remember being surprised they could ship a cart that inexpensively.
Yes, when I was pricing EE carts, shipping within the US (anywhere in the US) was $80 for the CTM & I'm sure Frontier was about the same. As soon as you have to have that cart shipped into Canada, though, the shipping charge goes up to at least $150 and then the UPS charges at the border were another $70 or $80 on top of that, not counting the taxes we would pay to Revenue Canada. Having my friend bring the CTM cart back for me was a (to me) HUGE savings--and especially since she was in the US long enough that she could bring back a bunch of stuff tax free....so I didn't even have to pay taxes. Saved me just under $300 not counting the lower price of the CTM.