If I'm not mistaken, a lighter flywheel will also let the rpms drop faster as well - nice at the track, etc. but maybe not as much on a DD. If it's significantly lighter than stock (and it's a car where the revs drop pretty quickly anyway between shifts) it could at least take some getting used to and you might notice you have to work it harder to go up a steep hill for ex.

If it's not significantly lighter though I wouldn't be too worried, but keep in mind I have no experience with aftermarket flywheels.