I have been using a Portrait 4 for about a year now and really like it, there is so much you can do with these
It is excellent for canopy masks, insignia, markings and camo (though note that it's usually a harder edge vs a soft)
My preference is for Tamiya masking sheets for canopies, and oracal 810 for everything else
I can usually get down to 1mm with good results
There are several ways to approach using them, but once you get the feel of it and know what works the results can be fantastic
The trace does work very well, I did purchase the upgrade so I can trace by colour as well as sometimes it will not trace on outlines
Not sure if I can link, but there is a forum for Scale Model Paint Masks with a repository of masks