My oldest ZZ is a 2014 Version 2 unit that I bought new and has never developed the hairline fractures in the upper links. I'm not a production climber, so nothing I own gets worn out very fast, and I'm very picky about taking care of tools. That said, none of mine show any wear that affects performance, at all. The V2 one is also my "loaner"... I've let dozens of people play with it, and shipped it all over the country. I was hoping one of the fatties would shock load it enough to cause the link fractures so I could send it in and get another V3 replacement. No such luck, it refuses to crack. It shows enough wear that you can tell it isn't brand new, but that's it. It's going on five years old, and I have no doubt that it will still be good for at least five more.
The best ropes for the ZZ are 24 to 32 strand double-braid or kernmantle ropes in the 11.7mm to 11.8mm range. Smaller ropes spread the links out further and I find that this makes them jerkier and prone to slight slippage... nothing scary, but they will coast to a stop sometimes... maybe six to twelve inches of slide. This probably is only with climber in the 200-lb. plus range. I go about 200 with gear, these days. I've never had a rope 11.5mm or larger slip. It slips very slightly with KM III Max, but that rope is about 11.1 or 11.2mm which is smaller than the 11.5mm that Petzl lists as the minimum rope diameter for the device.
Anything larger than 11.8mm and slack tending is affected. Some 16-strand 1/2" ropes will be usable, some add way too much drag. Two 1/2" kernmantles that I tried were both unusable, the added drag was just too much. One short hank of 1/2" kernmantle worked, but the ZZ didn't just fall down the rope like it does with the 11.7/11.8mm ropes... it would slide down about a foot and stop. That's still usable, but slack tending isn't the usual butter smooth. I've given up on 1/2" ropes with the ZZ, now that 11.8mm ropes are getting common.
I have the one V2 ZZ and four V3 ZZs because... well, aside from the obvious fact that I'm a bit weird, they are still the best MRT device for my needs, I climb with 2 lines most of the time, and I usually keep climbing gear in both trucks as well as the trailer I use when I'm doing tree work.
I also bought up a lot of ZZ V2 units with fractures in the upper links, for cheap, and sent them in for replacement. Petzl only asks for the serial number and your shipping address, nothing more. If it has the fractures, is within the 3 year warranty period (they can tell from the serial number) then they replace it with a V3 unit, and pay for shipping both ways. They don't care if you're the original purchaser, or not. I sent a total of 7 of them in, since 2015. I sold one, and gave one away as a gift.
