I haven't tried any of the others (I'm currently using a Z-Wave thermostat my utility company provided as part of a free energy-metering hub/package they sent me...they never said I had to pair it to their hub ), but I used to have a Zen Thermostat. Still do, if anyone wants to buy one used.
My only problem with it is that it seemed to do odd rounding with setpoints. For example, I'd set the setpoint to 55 degrees, and it would come back reporting that it was something like 54.9 or 55.1 degrees. This isn't problematic for most things aside from automations where you expect a range of values and have to plan a bit more carefully to accommodate possibilities slightly outside them. After a recent thermostat firmware update, it also seemed a bit wonky reporting or setting (I can't remember which or both) the fan operating state.
I'm curious how well the others work. I certainly like the look of the KONOz (not so much the price), but the Pearl was made by a well-loved Zigbee device manufacturer, so I'm sure it's not terrible. But as suggested above, mine is mostly automated, so as long as it works well with that, I don't really care.