I'm another Pro Oiler proponent. Why spend all that extra $$$ when other systems are cheaper? As others have said, it's fire and forget...but when you need to change the delivery due to dust/ rain/ whatever you can do so on the fly. Something that has not been said is that the Pro Oiler ECU has a logic circuit to automatically dial back the delivery when you are at a steady speed for a long time. This keeps from over lubricating and creating a big mess. Also, since the delivery is on the rear sprocket it is less prone to making a mess (unlike the wick method). Finally, Pro Oiler delivery is geared to distance, not time. When you are poking along at 35 mph the chain is getting the same lubrication (per ft of chain) as at 70 mph, not so with the steady drip method where you are almost over or under lubricating the chain. I have a Pro Oiler on my third chain drive bike. The two previous Ducatis got well over 25K miles on a chain and sprockets. I changed well before needed only because I was starting long trips and don't like to go on a 6-8K mile trip where I might have to replace chain/sprockets. I find that I can go from east coast to west coast with one fill of ATF in the oiler, that's about 250ml. I use ATF because it is a good rust preventer, slings off (taking grit with it), and is cheap.
Growing old ain't for sissies!