Very good.  

Product has very narrow window which is described, is not a full graphics suite.  However for the purpose of defining an exact pixel window and tracing by hand over anything it is excellent.

 Allows retro pixel rotoscoping  from Atari level to early 80s PC level to SNES and Hi-Bit era due to flexible window and variable resolution.  Very good if you want to capture character models for later sprites or do a direct trace.  

Free, but please spend a few $ buying it also to support the creators!