I posted at length about this in one of the fuel cell threads. People confuse the "fuel cell" with the box its mounted in. An ATL or Fuel Safe fuel cell is a Kevlar/Nylon bag that contains anti-vapor foam blocks and has an aluminum fill plate on top. That bag then gets placed inside a sheet steel or sheet aluminum box. The box then gets mounted to the vehicle in some way.
Other types of fuel cells (mostly drag race) are made like a regular fuel tank with a blow molded plastic "bag" containing anti-vapor foam and provisions for filling. That plastic bag also acts as the "box" that's strap mounted to the vehicle.
ATL and Fuel Safe fuel cells meet all racing sanctioning body safety requirements and meet all FAA fuel cell safety requirements. IMHO they are the only fuel cell you should be installing in your car if you plan to take it on a race track. For a street car, the stock tank or any of the plastic tank ones (Summit, Camaro LS1, etc.) are fine.