I never had a Leica Monovid 8x20 but I was reading the specification's on them and I am impressed that they are waterproof and nitrogen purged so they are fog proof also. I am also impressed that they have AquaDura lens coatings to repel dust and dirt. Also, the included macro lens is a plus for close up viewing. Neither the Zeiss 6x18 or the Vixen 6x21 are waterproof so maybe you would be better off with the Monovid if it is within your budget. The Monovid got 44 5 star reviews and one 4 star review out of 45 at B&H.