The mouth cover definitely took some getting used to - it felt a little claustrophobic and I woke in the night and removed it on the first night. BUT... my sleeping companion reported that I had been sleeping silently until that happened, a VERY unusual state of affairs for me.
So I tried it again the next night and it felt less strange, and I kept it on all night.
Since then, wearing the nose strip and the mouth cover in tandem, my sleep has been improved by about 90% and I will definitely buy these again and again