We have a Honeywell one...its not the smartest but I like it. We've pretty much always had it, we got it 2/3 months after we moved in. I think it does save us some money in that it heats when we want it.
First it has a schedule, so it knows the house has to be a least a certain temp between certain times. So we can say 19 morning, evening, 16 day and 17 night.
Plus unlike scheduling in the boiler, it only calls for heat when the temp drops below. Means it doesn't turn on all summer but we don't have to change it specially for winter.
Then it has geofencing, only set up properly on my partners phone as I wfh and I'm content with the away settings. But basically it has home and away, and so at home it follows the schedule, if you're away it has an away setting. Added bonus that the app notifies me when my partners phone has crossed the boundary. We've set it about 2 miles, I think, with the logic being it can start heating ready for his arrival.
Override on the boiler to turn it permanently on if something happens to the unit.
Unit is wired but has wifi so means we can place it anywhere with a plug. Allowed us to move it to the colder living room, from the landing next to the boiler cupboard (which meant it never decided it was cold enough despite it being freezing downstairs).
Finally, I can turn up the heating at whim, but it 'forget it' at next schedule so if I turn it up to say 21 in the day, it drops back into its schedule later so you don't have fiddle it up and down constantly.
Also, I can ask google what the temp in the house it and ask it to turn it up or down.