It sounds a bit dubious to me.
As far as I know, the normal UK mains voltage is 230V (used to be 240V). But it's allowed a defined tolerance (+10% and -6% according to a quick google). So to begin with it looks like this was originally designed for use elsewhere in the world, another quick google suggests that lot's of places, such as Canada, Hong Kong, use 220v Mains. UK stuff has to work at 220V as our own mains may occasionally drop to that level, but 230V remains the standard, so I would assume that apparatus sold for the UK would be optimally efficient at 230V
If the device is acting as a switch-mode regulator that regenerates the mains AC at the exactly correct national voltage then I suppose it might in some circumstances it might allow things like fridge motors to run at their optimum voltage, and hence optimum efficiency, but only if they made a UK version for 230V.
More likely, I suspect it's just a step-down. That would have all the drawbacks already described by Eric and Orainseer, and it would also cause big problems for folks like myself. We live out in the sticks and every year, when cooking Christmas dinner, my oven seems to under-perform with embarrassing results. It's OK the other 364 days a year so I suspect the cumulative load of Christmas dinners all over the county brings the voltage down to the legal minimum, which is to low for my oven. A step-down transformer would make that much worse.