I tend to compromise it.
I use a test stand to run a few tanks through a new engine as well. But I basically get the engine adjusted on the stand to ensure it is working OK, get familiarized with it, et cetera. Then after a few tanks to limber it up a little, I switch it over to a airplane and finish its break in flying it around. Some engines take longer to break in thus the engine might need a long time getting run in and in the past I used to use a test airplane to fly a new engine for a while to break it in. Then I would install the engine in a airplane I got the engine for in the first place. I have had some engines need a couple three gallons of fuel to get them broke in good. They were quite tight too, you had to break them in for a long time before they ran good.