Like hogcowboy, I'd do as the manual says. I am a big believer in manuals for any expensive or potentially-dangerous items like motorcycles, cars, guns, even computers and other electronic devices. Before I even decided to buy my 2019 Kawasaki Z650 I had downloaded the owner's manual and read it.
Nothing wrong with changing at 300 Miles , I have changed mine as early as 150 Miles after doing an Engine Rebuild knowing that the Rings were set well and taking a good look at the Break In Oil have no regrets of doing so ..
Might be driven by the materials or coatings used. Oil changes are extremely cheap insurance. For break-in procedures, I'd always follow the manual. A good break-in gives the bike a better start on longevity and good performance. (And that's why I only buy new bikes. You never know how the first/previous owner treated the bike during break-in.)
Mfgs do the best they can, but there will always be the possibility of small metal shavings, or parts getting 'shaved' during the break in process. When you have new metal rotating against each other (think bushings, thrust washers, regular washers, etc.), they have to settle in and get seated. If you don't change your oil on a new engine, those shavings will scar the engine. Just do like the Mfg says. Very cheap compared to a new engine.
Yeah is MC going to replace your engine if something happens? :surprise:
I can't stand the ones that respond to a break in question with: "Drive it like ya stole' it." (Which they probably did.):smile_big:
I have always thought that the engineer's working for Honda, Yamaha--Harley, Indian and all bikes know more than 'Joe Blow' down at the filling station where he has worked for 30 years:surprise:
Not all bikes call for a 300-600 mile first service. If I recall, my last new 2012 Goldwing's first service was at 4,000 miles, then every 8,000 miles.:grin: I changed the oil and filter at 500 miles and then every 4,000 miles using ultra premium oil.:smile:
Break in hasn't really been a problem on 'modern' bikes as the RPM limitations allow lots of bikes to be ridden at normal highway speeds during this period.:smile:
When I used to buy 2 stroke street and track/ desert bikes, the break in period was extremely important to aid longer piston, cylinder and ring life. Race bike builders like myself used to run their CR500's, It465's, RN400's or Bultaco's and CZ desert bikes like I raced for a short 1/2 hour at slow speeds and then take the top end apart and look for 'HOT SPOTS' in the cylinder and polished rubs on the mating piston and use like 800 grit metal sandpaper to polish those 'HIGH' areas down that can lead to seizures :surprise:
No one I have ever known has ever had an oil related failure on a 4 stroke street bike although using 'fuel conserving' type oils made for automotive use can cause a clutch to slip.:sad: