Oh my, that is not good, not good at all. If you want to pm me the location where these techs were I would really like to notify Safe Kids. That is terrible information and NOT correct.
There is NO difference in safety between a Britax seat and any other. And there is nothing about a Britax seat that makes it safer to turn a child forward-facing sooner just because they're in a Britax. NOTHING.
And there is nothing in the CPST curriculum that says that, they are simply making things up as they go along.
That said, I am thrilled that your dd is rear-facing now, and that she is happy! It seems, then, that being so reclined was at least part of the issue and, I hope, that you don't feel the need to turn her too quickly. You have, most likely, a 40lbs rear-facing limit on your new Marathon and I hope you make good use of every last pound of that!
Coleen
CPST