I have had them in the past [on more than 1 machine], but don't like them; and I do serious touring miles per year. Using a spray lube frequently is much better in my opinion.
They have a fundamental design flaw too - they are vacuum operated, but as vacuum decreases with throttle opening you end up with an over oiled chain around town and an under oiled chain on long distance high speed jaunts.
Oh and most are fitted badly, usually bodged in by dealers in a hurry to get it done.
edit: the electronic versions eliminate the vacuum operation flaw, but are more £££.
