The A&D Fx-120i scale with AutoTrickler/AutoThrow is the best available, and it can reliably throw charges to +/-0.02 gr even with "difficult" powders; the downside is that it costs nearly $1k, but it's worth it. If you don't need/want that level of accuracy any of the major manufacturers' units will do the job. All of them have their quirks, so it pays to do a bit of research before buying.