A lot depends on how well the flat is insulated, and whether it has other flats above / below / one or both sides.
If it is a flat with another above, and another to either side, I wouldn't bother. The money you'd spend on the controls would be as much as you'd save (at current gas prices) over several years.
If its not so well insulated, then:
a. If you live in it, you could install the weather compensation. Its very fiddly to work, and unless your boiler is a combi I'd strongly advise you to have separate hot water and central heating times.
b. If you let the flat out I wouldn't dream of installing weather compensation. You'll spend your life on the 'phone explaining to the tenants how to work it.
They work (broadly speaking) by using the outside (North facing wall) temperature to determine how hard to fire the boiler to ensure the inside of the property reaches the desired temperature at the required time. They use a "heating curve" over which you have some control to determine the rate of heat loss from the property for a given outside temperature. The system "learns" over time how your property reacts to changes in the outside environment.
You would save gas as it is more efficient, but whether the savings would outweigh the supply and installation costs is another matter.
The VRC470 can go anywhere inside the property. However if in a room with a TRV, then that TRV should be set to maximum, otherwise the TRV and VRC470 could "fight" each other.
I've got the weather compensation set up with a heat only boiler. It has saved quite a bit of gas over the last four years, but it is a pain in the rear to set up and operate. I'm often tempted to get rid of it and install a standard programmer and thermostat.
