I destroyed the bearings and the sprockets of TZ21 in around 8 months, but I used it every day in all weather conditions – had it on my year-round commuter bike that I use in the snowy and slushy winters. The backside of the freewheel is very exposed and water gets inside easily, so I would recommend you to put a spokeguard behind the freewheel or regularly clean and put some dirt and grit repellants on there if you decide to go for TZ21. Overall, I went through two chains on that freewheel until the teeth were worn down, so the metal is rather soft and prone to rust (started rusting after a week). Can't comment on the other one.