With the COVID-19 pandemic some new attention has come to mask wearing pressure injuries. On a very general level, pressure injuries happen mostly to immobilized patients or those with sensitive skin, such as early borns or babies.
That said and as an aside there is the NPIAP which is a society exclusively concerned with pressure induced injuries: https://npiap.com/
I couldn't find any specific information the referred mask model, however, here are some general guidelines issued by the NPIAP to prevent pressure injuries. They include
- relieve pressure when possible
- reduce pressure intensity when possible
- avoid moist (softened) skin
- avoid friction
Pressure is defined by force exerted on an area, therefore it may also be a good idea to increase the area therefore reducing the force applied to the area.
For COVID-19 there is also a position paper on N95 masks: https://cdn.ymaws.com/npiap.com/resource/resmgr/position_statements/Mask_Position_Paper_FINAL_fo.pdf
There is some more information on prevention and some general information on therapy for pressure injuries here: https://www.uofmhealth.org/health-library/abp5591
These are not specific to masks and involve recommendations such as rotation the places where pressures is applied; this is mostly applicable to immobilized patients. For these patients rotation of their bodies so that the body weight pressured is applied to different regions of the body can be beneficial. A takeaway may be to try applying pressure to different areas of the face, such as using different models of masks over time. A strategy with stenomasks may be to have at least two different models so that they can be worn alternately.
As for the quality of air: I assume the air surrounding you when wearing the masks is relatively clean and breathable to begin with (otherwise a different kind of mask may be necessary). As far as depletion of oxygen and enrichment with carbon-dioxide goes, I assume that the stenomask will have to have passed some testing that will prevent CO2-intoxication when used for prolonged time. There may be some information on this in the masks' manual. If someone has a link to that, feel free to post it in the comments.