It all comes down to what is most important to you and what features and components are more desireable to you.
The FFR...
If you just want to install a modern 302 with fuel injection, and a 5-speed, and don't care about what differential you use, the FFR is a great value. The shape is still a little off, but getting better now. They are really quick too being so light weight and all. I don't want to go on a tangent, but the shape, rollbar, dash, rear quarters, are just off. Functionally, this is a great car though!
The Unique...
If you are looking to build an FIA or 427SC car with either a 351 or FE 390/427/427 and are stuck on having a more original Toploader 4-speed, and want the original style Jag IRS rear configuration, the Unique is a great value and is very hard to beat. The shape is not perfect, but its very close to an original. The glass work is nice, and they look great if body-prepped correctly. The Carrera adjustable suspension and rear tri-bar stabilization system is a nice feature too.
Of the two, and for street use mostly... the Unique is definitely the more authentic looking car, and the UM Deluxe pallet kit is a nice way to go if you don't want to have to build one from scratch. If you had a donor Mustang for cheap, and didn't care about making the higher $$$ upgrades, the FFR sure is a nice way to get into your first Cobra. You could always sell the FFR and upgrade later too. Compare both on a spreadsheet, upgrade vs. upgrade and see what your total is. My good friend added up all the options on the FFR, and it turned out the Unique Pallet kit was a better deal for him. He was looking for something more authentic looking. Sorry, but I'm very partial to the Unique over the FFR for asthetic and component reasons. For the track, I'd seriously consider the FFR just because of the no-brainer and low-cost components that are used and are easily replaceable...
just one person's opinion. Drive in both and compare to see.