How many TRV’s are you using ? Without those on each radiator its useless, and a Nest would suit you better.
Evohome is only really cost-effective when running over multiple zones. We have it running to 6 zones over 3 floors on 11 radiators with the hot water (1 x Control panel, 11 x TRV’s and 1 x HW), and if you’re using the control panel or app regularly then its probably not optimally setup - a good heating system is one where you’re comfortable and never need to touch any controls.
It extremely clever in knowing when to turn off the heating late at night, based on the heat loss in each room (measure by the TRV’s) etc… Similar smartness in switching it on early in the morning, so its warm when you’re up.
Forget about ST integration, use IFTTT with the ST presence sensors to turn it off/on according to occupancy.
In terms of updates, the control panel has regular (annual) firmware updates - the latest version now includes outside temperature and there’s another due soon which (its in beta) uses the external temperature in calculating when to turn things off/on.
iphone app is fairly steady as well, never crashes or logs me out.
The user-interface is a little old-fashioned, but if you’re using it regularly then its not optimally setup.