Grout sealer enhancer does work. If you lay a thin layer of it over your grout lines, you'll be sure to give yourself less maintenance in the long run.
Grout sealer enhancers do definitely work. The use of sealer enhancers on grout not only brings out the color of the grout but it also helps the grout avoid discoloration. Grout sealer enhancers may not work as well on certain grout colors, but will enhance usually any color it is used on.
Depending on the brand it will have different results. Most will simply make the grout appear darker. So if this is what you are looking for you should try it.
Grout is porous and thus the need for sealer, to keep liquid out. Use the brush on type sealer, 2 coats should be applied an only on glazed tile since glazing is the process of sealing the tile.
No, I've tried several different brands on my tiled kitchen counter and none of them have held up to the test of time. Perhaps, it is the moist environment; but a tiled bathroom would also be moist so I am not sure that is the reason.