I did not want to go for a Scottoiler because they require their own special oil while the Pro-Oiler can go with normal motor oil, gear oil or whatever else is available.
Ime, motor oil or gear oil are crap final-drive chain lubes, I get so much with a Scottoiler I can't remember the last time I bought some on its own.
makes a lot of sense to me to vary the dosage of oil based on speed rather than time or engine vacuum.
You misunderstand how a vacuum-operated Scottoiler works. Irrespective of what speed the bike is travelling at, either the rider constantly varies the throttle position very slightly, even unconsciously, or the fly-by-wire does to maintain a set speed; a vacuum-operated Scottoiler responds to all of these.
But modern chains chains last 20K miles with minimal lubrication.
Is that all? Or is "minimal lubrication" the problem?
The oldest Scottoiler lubed chain I have has covered about 15,000 miles, the adjusters are about half-way along.
More from my pov:-
. That chain (and sprockets) are 27 years old. If I get home with a dirty/wet bike and I don't get to clean it for a while, the dirty/wet chain doesn't turn into a corroded steel bar, because the chain was being lubricated all the time up 'til I stopped the engine outside the garage.
. If I don't get to ride the bike for whatever length of time, one thing I know will still work without any attention is the final drive.
. I don't have to buy "premium" chains. While that first one was an O-ring, Fraser Scott advised that a Scottoiler would give cheap chains the same long-lived protection. Ime, he's right. Afaict, the key is the constant lubrication - chains are precision engineering, same as the bearings inside the engine; one reason we don't rebuild engines every 20,000 miles is the bearings inside it are lubricated constantly with clean oil?
. Riding long-distance, one thing I don't have to do in the evening or the morning is faff around spraying the chain. Mate O'Mine visited on his Speed Triple last summer. Jeez what a pita is lubing a chain without a centrestand - two grown men to spray most of a can of chain lube on a patio.
Swmbo is still displeased.
. I've yet to replace a Scottoiler-lubed chain.