We used them for the first time last year and love them. We only calve 40-45 calves, but they are low stress on cows, calves, humans, and fences. We were able to wean certain groups of calves depending on need. For example, all sale calves were weaned during the hottest time of the summer without having to lock them up in a barn so they wouldn't flee the scene. We didn't encounter any sickness and didn't have listen to calves or cows.
Of the 42 calves we put them in last year, only 2 got them off. They were replaced the day we found them and they never came out again, which tells me we may not have put them in good enough.
We ordered from
www.quietwean.com and they cost us with shipping under $3/each.
Depending on your vaccination protocols, it will likely require an extra trip through the chute, but we got pretty good at taking them out of our sale calves when we had them tied up. The non-sale calves had to go through the chute the extra time, but it was well worth it.