i've used the 3 step system in my honda's and it works well.
if the car is running smoothly already, you won't notice a difference, but you notice a bit of visual improvement if you take the top end apart. in my case there was some light/medium deposits on the valves and on the tops of the pistons. after treatment, there were some very light deposits, but let me reiterate, my car was in decent mechanical shape and i noticed no improvement whatsoever. i even reset the computer and let it idle on a level surface for 10 mins to reset the operating parameters (so sayeth the service manual).
in my case, i just felt like trying it. i've also tried the berryman 3 step system. it's a very similar system, with somewhat similar results.
for some reason, while the 3m system is a bit more expensive (you have to purchase or rent the tap with hose to connect to your fuel rail), i like it better. the fuel system cleaner worked GREAT.
i noticed that the fuel level sensor was a bit slow at times and while using berryman's it didn't help. when i tried the 3m as part of the kit, it only took one tankful to notice a difference. of course, i'm no scientist, so the sensor could have decided to start working better on it's own, but i was sold.