Amsoil makes one of the best on the market. To add one can to 15 gallons of premium, it will actually only raise you up one point, but adding the same amount to 15 gallons of regular, will raise you 3-5 points. This is what the tech dept. at Amsoil told me. It is most effective when added to reg. fuel.
It would stand to reason that a company like Amsoil is not going to put a bad product on the market, but I think much of whats on auto supply shelves is poor quality, especially if the cost is low.
Some octane boost formulas, leave a dylectric coating on the plugs, and can cause the plugs to not fire properly.
I have used this in my old Chev PK that has the timing set for premium, and will ping and clatter when using regular. One can of this to a tank of regular stops the ping and clatter completely, so this tells me it doe's work in that sense. So should premium become more scarce, this would allow you to atleast run the car, safely. The Viper will run on 91 octane so that tells me the timing is not very aggressive. Supercharged cars be carfull. As Paul said it's a poor substitute for Premium, and I think this to be true. You can loose an engine on forced induction cars from lack of octane. Hyperutectic pistons are not as forgiving as forged ones.
Warning 04 and back Vipers do not use knock sensors, to the best of my knowledge. I think 05's are running them. Reg. fuel on a heat soaked engine, could damage the engine. If your running a comp. upgrade, such as VEC2 the timing is advanced more than stock, and you will have a problem, so watch out.