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I've used the run it in hard method on new OEM engines as well as built engines for car and motorcycles for the last 30 odd years.
I've always had excellent performance and longevity whether they are daily drivers or race engines.
Only risk factors really are who assembled the parts and quality control on parts, if a engine is built right it shouldn't, and doesn't break, if it does break, why did it break, typically I've found it's from poor assembly practises, faulty parts or poor tunes.
As for "manufacturers recommendations", can you imagine the issues, "I was boosting up and down the road out the front of Toyota following the manufacturers break in recommendations.....officer".
My current car, a 2017 86, was broken in hard on the day I picked up my car from the dealer, it was NA tuned as soon there was dyno time, and it now runs a AVO turbo.
The car runs like a Swiss watch and uses no oil.
Engine oil was changed after the first 100km (5w30), then at 5k km intervals.
Drivetrain oils were changed at 500km.
Car gets abused daily, no broken engines, no broken gearboxes, no blowby issues that would require an AOS.
My car before the 86 was a STI, same hard method was used, no cracked ringlands or dead kittens.
My next car???, but a hard break in will be utilized.
But like everything, opinions may vary
The important thing is to do some mad skids regularly.
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