Used Z-tags for 25 years; found them far better than any of the two-piece that we'd had in the past.
But... you absolutely can tear an ear putting them in, if the cow/calf is throwing their head around. We had a bunch with one - or both - ears torn, from someone who will not be named manning the tagger. Me... I just put 'em in backwards way too many times. lol
We also used z-tags for a couple years.
We had just switched, found our two years later all numbers disappeared so to speak.
I got in contact with local sales rep who explained problem they had with printing etc.
While in this process he also explained that the calf tags that had been manufactured had a one in each ten made had a defect. Which he explained would result in tearing of the ear as it went through. It seems the point would be blunt/fold over due to a molding issue.
That was exactly the rate of ripped ears we had in calf's using these.
In response
Z-tag replaced all our defective tags free of cost, as well sent us some calf tags free of charge.
But the rep, who is also a cattle producer convinced me to go to their two piece system.
Sent us a free tagger as well.
We have had zero issue with ripped ears since, new cow tags with lazer engrave holding up.
Would recommend go to two piece system.