Bosscreens are highly atypical focusing solutions for large format cameras. They're composed of a layer of paraffin wax between two pieces of glass, and this results in the positive in-&-out snap of ground glass but without the presence of grain. Using a loupe to fine tune focus with either traditional groundglass or "bright" screens can be frustrating, because discerning if you're looking at groundglass/fresnel grain or your subject is often quite daunting.
Bosscreen is less affected by off-axis viewing than typical "bright" fresnel screens, which often black out when you displace the camera's standards with shifts, tilts or swings.
Bosscreen is not designed to be used in extremes of soaring heat or freezing cold, but can nonetheless be easily employed in those scenarios. If it is treated with the same rational precautions you'd give to your film or sensitive digital recording equipment, you can expect a lifetime of perfect performance.
Each Bosscreen is designed for a specific camera type application to assure that the net effect of its use does not affect the placement of the focusing plane relative to the film plane. If you've already calibrated your groundglass for your particular combination of camera and film holders, substituting a Bosscreen will not negatively affect this accuracy in any way.