I have no experience with physillum husk but believe flax hulls would be the same. You do need to drink lots of water and flax hulls do bulk - so maybe the same?
Sorry, dont know about mucoid plaque. Have not had them before and dont think I have them now. I use the flax hulls with a good probiotic (friendly bacteria) and it has been very good for me. Reduced a small cyst in my ear lobe within a week. Other than that, no significant health problems. I use it more for "preventive" purposes.