cutting crown molding

It works.  For someone that is adept at using a jigsaw, it would help you produce a nice coped profile in most crowns.  I used it on some large MDF crown with a couple intricate details-turned out nice.  The tool gives you a platform to ride the jigsaw on while moving in and out of the profile.

I have watched the developer of the Collins Coping Foot-the jigsaw base that can be fitted onto a (bosch) jigsaw to aid in coping.  He makes it look REAL easy to make the cuts.

Both of these have videos of their operation on their sites-easy to find via google.

Then there's the angle grinder with sand disc method.  I've done this a few times but most always fall back on a coping saw.  If I was doing more than one room at a time I might take up one of the non usual methods.