I’ve been using a 1/4 hp Flexible Shaft Machine by Eurotool to prep my next “large” project a Vanaheim pattern Griffon. The model itself was heavily warped from heat during shipping but additionally the casting has very large sprue connection points and flash. To speed up preparation and clean up I used an emory cut off wheel and a coarse grinding drum. This cut down an hours worth of clean up into about ten minutes worth of work. More importantly I’m able to cut closer and with more control than I can with traditional hobby saws.
It isn’t a must have tool but if you find yourself working on large resin models regularly it is very nice.