Is the wireless room stat much better?
Having had a nightmare with one radiator SRT which was basically useless and over reading then under reading and keeping the room cold when it could call for heat I switched to independent. It was better but it had a -2.5C offset and the room temp had to be set between 22-23c to get 20c first thing and it would slowly creep up to 21c by the late evening. In the very cold weather it would often be around 19.5C only in the room by early evening which is far too cold for sitting in.
I added a wireless temperature sensor. Set the schedule temp to 21C so it could call for heat and then watched how the room temperature fell even though the heating was on 🙄 So the calling for heat mode still has the radiator output too low. The main house temperature rose well over the set point. I left it a few hours. Still not up to temperature. It was like the radiator was suddenly too small for the room.
Set it back to independent and the radiator is turned up so it grabs heat when the heating is on rather than constantly asking for more heat but not turning the radiator up enough. Required room temperature reached easily. The house temperature also doesn't rise to compensate so therefore when it's independent it actually works intelligently and sends the heat where it is needed. Which is what a dumb old TRV does (!)
Wireless room stat helps a lot with these SRTs but they don't get around the calling for heat issue whereby the SRT just doesn't turn the radiator on enough.
I got a room stat when it was offered as a refurb for £50 including delivery which is a more reasonable price.
The lack of stand I solved by using a cheap tablet stand that I already had.
The wireless room stat makes a big difference but the biggest difference seems to be in using independent mode. The radiator SRTs actually function more intelligently. When both are wanting heat then it does seem to trigger the heating to come on long enough for them to grab some heat quickly to bump the temperature up. It's far more effective than the heating coming on for ages and trickle heating the room instead if you have the on/off heating. It feels like it's more efficient and less gas is being wasted.
I think many people run a mix of radiators with the SRTs and ones without so what works for that might be different to someone using the cleverer openTherm and having SRTs on every radiator so the heating is running longer but at a lower temperature. I have another SRT on a radiator that is on an outside wall. It's not as inconsistent and weird as the other which is on an inside wall.
I'm sure someone with a smart meter could run some tests on gas use to compare whether one strategy uses more gas than the other.