We run them in our short coarse cars, no problems, I think they are great seats, currently putting them in a desert 1600 car as well.
In that case, my reservations are lessening, but in SC, one is in the driver's seat for considerably less time than is typical of desert racing.
Are you questioning them beacuse there FX1's or because there a Tub seat? If its because there a tub seat then you need to do some research.
Anyone using the Corbeau FX1 seat? seems like a cheaper alternative to the Sparcos.http://www.corbeau.com/products/fixed_back_seats/fx1_pro/
Corbeau has been around since 1964, so I doubt that any of thier products even come close to having no regard for safety.
While the seat does have a mount for rear support, it may not necessarily need it..but as stated, some organizations require it if there is no rating, thats why its there.
Just because a seat doesn't have an FIA rating, doesn't mean its made out of styrafoam. An FIA rating is a certification by an independant agency. To obtain this rating costs big money, which is then passed on to the price of the product. This is done because some sanctioning bodies require certain products to have a particular rating, and some racers want what is garunteed to be the absolute best. However, almost all manufacturers make products that don't have ratings, and I would guess most their experience and r&d goes into these seats as well. Basically the FX1 is a copy of of the Sparco Evo. My .02