Many years ago I felt that prime lens were the only way to go as zoom lens just didn't produce the same quality. I'm pleased at admit that I'm now very wrong in that assessment. I have used a combination of Mamiya and Phase One lens for several years with each lens being a prime. This lens now replaces 3-that were in my camera bag; 45mm, 55mm LS and a 80mm. The 40-80 not only physically replaces 3-lens it also adds more focal lengths between the 40 to 80. The lens barrel is marked 40, 50, 60, 70 and 80; of course you can shoot anywhere in-between the numbers.
The first thing I noticed in testing/getting used to the lens is that moving the zoom ring to each focal length marked was dead on the money which is something I like when I want to shoot a specific focal length say 50mm. Speaking of focal lengths, the 40-80 is equal to 25-50mm in 35-mm terms due to the difference in sensor sizes.