I'm just about to have an iT500 fitted in my house. I'll report back.
I have fitted Heatmiser neostats, Honeywell, nest and I have the Salus it500 in my house.
It depends on what you want from a control point if Veiw. The Honeywell is very good, you can use there thermostatic valve heads and control each room. The hot water control can control temperature. ( why you would feel the need to alter that!) it's very intuitive, has a nice controller, but is expensive.
The neostats are very neat. They ate very good at long distances between the stat and router, as they can link between thermostats. They can control up to 32 zones and have a separate hot water timer. The app is in my view the easiest to operate.
Te nest is quite simple in operation. But as my brother designed the software for these. I have a great suspicion of there snooping of your habits. They were designed for the American market originally to try and predict electricity demand. I find they can under, or overheat on a warm day following a cold day.
The Salus it500 is again easy to use and set up. It has hot water timing on the one unit. The app is not as good as Heatmiser, but still good. For the price you can't beat it.
Summing up, they are all reliable theses days. Customers like the techie bit and they are easy to use. But. Tbh in the two years I have had mine I've used my phone to switch it on remotely 4 times! One of them was because I couldn't be bothered to walk 6ft to the stat?