MS in engineering is VERY different than other academic tracks. For most disciplines, you get a MS when you don’t pass qualifying exams and wash out of your PhD. It’s not that way in engineering. A MS is a way to deepen technical expertise without narrowing with a PhD. It comes with a bump in pay and broader attractiveness in the job market. Our son finished a BS and thesis based MS in ME just after his 23rd birthday. He walked debt free. It was an enviable position to be in.
The issue with switching from Physics to Engineering is that there might be some backfilling. He’s way ahead though, so that won’t be a big issue for him should he choose that route.