In my experience the vacuum operated one was utter **** that I'd actually take the bother to remove and bin if a bike ever came with one. When working it sprayed gallons of overpriced sticky oil all over. Fortunately it soon leaked down and lost it's prime and ceased to function. Re-priming was a half hour, mess, noisy horror of a job.
Compare the time and costs and I'd say it was about even. The Scotoiler is a PITA to fit, takes longer to fill, has exposed components (tiny little tube near the chain) and costs the same to buy as the extra chain you might get through in the normal service life of the bike. Shaft is a lottery, change the oil as part of a big service and you save time and cash over the chains, but get a failure and the savings go up smoke big style. Yamaha Tenere or on a Guzzi I'd entertain it, on BMW's it reduces their chance of selling me a bike.
I think the advances in chain technology and spray cans in the last ten years send Scotoilers the way of tinned wax you had to boil up on your mums stove. Non-sticky spray can every 500 miles and a clean down with kerosene at the oil change/adjustment interval for me.
Andy