Central Heating Room Stat - Smart or basic?

General Discussion

During a quarterly check I walked into a property which was subtropical in temperature.  Initially I thought the tenants (limited English speaking African) were enjoying the heat but it soon became clear the Drayton digital room stat had been set to 30c and they couldn't reduce it.  Hence why all the windows were open.   The roomstat was madly complicated to use even after I had down loaded the manual for it.  I gave up.

Does anyone have any advice on using a Google Nest or British Gas Hive smart system?  It needs to be simple to use ( possibly with the app offering foreign language options ) and ideally subscription free.   I have thought about reverting to a Honeywell manual dial oldschool but think this might negatively affect the EPC which is due next year.