...I asked the same question for a long time. Then I bought a faster hydraulic Mec loader that already had one of these counters on it.
It just never occurred to me how helpful a counter would be, till one Saturday morning when I was late getting to the club shoot...and had no ammo loaded. 15 minutes later I headed out, knowing I had enough to shoot the event without having to spend time to count them and be sure.
...I thought that was pretty cool...but then when I wanted to load a couple of hundred shells...I began to realized how much I would just glance over to the counter to see where I was at.
To make a long story at least a little shorter...I have since purchased all Mec hydraulic loaders...and the first thing I got for each one was a shell counter. Just tooo convenient...and I really never dreamed how spoiled I was till I bought the second loader which "didn't" have a counter. Unbelievable..!
...and it only takes about 5 minutes to mount one...just too easy.