Having a chain oiler is just another thing on your bike that could go wrong. Not to mention adding more weight (if your into that) to your bike.
I see they have merit but call me old school - "O" ring chains, a clean every now and then and a adjustment check and lube every few rides job done.
I think your more likely to spot trouble with your chain if you do the mandatory check/adjust/lube every few rides. I know a mate has an oiler on his jap machine and he thinks that he doesn't need to worry about the chain until things look very obvious.
Crazy talk I say!