well i have bought their HVS MR, and hot ina zma pocket(aka hot pocket) a long time ago.
when my car was still an auto with just the HVS the car felt more snappy, car started up faster, saved a little more gas with daily driving. as for the hot pocket i felt a increase again in a more responsive car, and smoother shifts(auto).
as for it being in my 5speed car now. after taking them out, it feels like a whole different car. i say if you can afford it to get it. if not look on their site at the hot pocket. plugs into you 12volt socket, cheaper than the HVS, can be used in any car.
i have nothing but good things to say for their products, because they really do work. only downside is their prices....