they hit me with this. struck me as a load of rubbish so i checked with an refrigeration engineer .
they claim it refreshes the refrigerant but you don't have your fridge serviced every year. the refigerant is closed loop, so if its low or escaped you have a leak, it also has no shelf life.
they also claim to squirt a lubricant in the system. the enigneer i asked said refrigerent is naturally lubricatating and the compressor bearing has sealed grease.
so providing the system is in good shape, as far as i can gather its a complete waste of time. i think it probably a good idea to run the system once a month to prevent the compressor siezing, but otherwise if its working leave it alone.