Installed correctly, they're great. Better puncture and leak resistance in the event of something bad, you can have them placed as you see fit/have space, they can be internally surge tanked, prefitted with an fittings and all that other good stuff. To go with all the upsides...there are dilemmas in a street car: Off the shelf cells won't fit the stock location. This means the cell will have significanty lower capacity as they are typically squares that have to fit in the passenger side only, or they are tire well cells. Well cells require a firewall as we have hatches. No firewall, no track time. To fit the stock location (sort of) and keep capacity, you need to remove the spare tire well and weld up the floor. The fill neck is also pita, again off the shelf are almost always top fed, and will either have to be in the hatch, or have to be fabricated to have an external fill.
You could have a cell made that matched the stock tank shape...but a factory tank would likely be cheaper.
