That's correct, the Mountune MT upgrades are approved in such a way that they go onto the insurer database.
Had right fun and games a few years ago trying to insure my ST when it had the MT kit, insurer was adamant it only applied for cars factory built with the Mountune upgrade and not dealer fitted
I think the mountune is good if you want to keep the ford warranty intact, if the car is outside of warranty you can probably get a very similar kit for less money.
I may look into mountuning my facelift ST mk3 in the future but it isn't available yet due to the slight change in the engine layout and map over the pre-facelift.