Breaking-in involves successful heating and cooling of the engine parts so they mate correctly from theoretical tolerance to "real" tolerance. Its a one-time event....changing fuels does not cause the metal on the engine to suddenly "reappear" to be rebroken in again. What changing fuels can cause is "old" cold carbon deposits to free loose and result in sudden "unreliable" performance...but this shouldn't happen on new engine where there is no deposits yet.

I think they are trying to get you to join their super saver club.

Definetly doesn't sound right and I'm getting ready to buy one of these. Any other symptoms? You tried basic things. You unscrew the needle value and look at it with a magnifying glass? Tried a different glow plug? (sometimes they are bad right out of the box...I had one that was brand new but one side of the weld was broken and barely making contact but enough to pseudo work)