I've been the one shot, clean, etc,,, break in process in the past and then, I've gone out and bought the least expensive FMJ military ammo that I could find and shot 100 rounds before cleaning...I can't say that one practice is better than the other...
Since yours is a .204, you are stuck with factory or handloads, but regardless, my .204 AR didn't get any special break in, but it's a custom XX Match grade barrel and is exceptionally accurate from the first round..
I've read reports that indicate that barrel maker promote the idea with the hopes that you will wear out the barrel quicker with all the scrubbing, but don't know that it isn't an internet myth...
Unless you are paying for a hand lapped custom made barrel, most will have microscopic tool marks in the surface that have to be 'smoothed' out or 'burnished' before real accuracy potential is achieved...