the first option requires less time abroad but unlike with other visas, the requirements for in-country switching to non-B are a little heavier than abroad, so various companies kindly ask prospective employees to stay abroad for some time.
So, if it's a respectable employer, it gets you a free trip to a neighboring country 😊
your prospective employer sounds serious and knowledgeable about the matter. I trust they'll guide you through the process. As any respectable employer would, by the way.