Underdrive pulleys

Do underdrive pulleys really cause unnecessary strain on the engine or is that true only with certain types? Do underdrive pulleys get significant gains for preludes?

i've heard it makes the car idle rougher but i dont know if thats with certain types or not

As far as I know Underdrive pullies (a/c, p/s, & alternator) do not cause any extra stress on the engine. You get into putting extra stress on the engine when you talk about crank pullies due to the aftermarket ones lacking the harmonic dampner.

As to gains due to underdrive pullies...no they don't seem to do much. I got, I don't notice a difference besides the engine bay looking better.