Compared to the App, the skill is far too inadequate. I suggest the following additions/changes to the skill.
(i) Have a "Query [device] status" which would return a vocal on/off status
(ii) Allow setting of timers and schedule through Alexa. eg. "Turn on water heater everyday at 7am for 1 hour" or "Switch off lamp after 10 minutes"
(iii) Allow temperature/humidity based triggers for Sonoff TH modules