Right now the main differences between the ZEN22 and ZEN27 are in the hardware though TSH is still selling ZEN22 without scene control so if that's important to you go for ZEN27 or be prepared to manually update firmware for the dimmers.
Here are the primary hardware differences:
http://www.support.getzooz.com/kb/article/151-zen22-ver-20-vs-zen27-whats-the-difference/
One other thing to pay close attention to is that the ZEN27 can only handle up to 100W of LED's max (with both sides of heatsink tabs on) so if you have groups of 6 LED's of more you'd like to control, go with the ZEN22.
Non-dimmable bulbs will flicker with the dimmers when turning on and turning off so we recommend using our dimmers with dimmable bulbs only.