I tried it for 2 months or so, but it's been a while. Never really got the hang of it. It's a totally different handling philosophy compared to GMAX / 3DS Max.
For FSX there seem to exist a few scripts to export mdl files in the meanwhile - don't know if they support animations though. When I tried it I exported as Wavefront OBJ and did the post processing in MCX - but I used it for non animated, static models only.
Cheers,
Mark