Bought this foot-switch for my ENGL Invader and it works perfect.
I use it to control my amps four channel's, gain and brightness settings, FX loops and I'm able to switch anything with one switch stomp, so that's perfect for me.
Z12 has 0-9 preset banks and at first it might seem it should have 10 presets for each bank, however that's not true... 00 preset does not exist, so when you select bank - 0, switch nr: 0 does nothing... However that didn't gave me any difficulties using it efficiently (I try to avoid bank 0)!
I also use it on stage and don't have any difficulties using it, however I think if the stage was very dark I might ran to some issues... There could be LED indicators for each switch (which do not exist) since that would make easier to see when it's dark on stage...
The body is made from metal and I suppose it would be very hard to break it.
I would recommend Z12 over Z6 or Z15!