Does anyone know if there is a safety benefit to using a convertible/3-in-1 type seat in booster mode vs. a high back booster in booster mode?

We have been doing lots of car seat swapping with our crazy childcare this summer and my daughter has ended up in our EvenFlo Big Kid a lot. It’s a great belt fit, but it just seems so much flimsier to me than our Britax Pioneer which is like a tank. When she transitions to a belt positioning booster full time (still not quite there in my car as she falls asleep on longer drives still) I want to give her the option between the 2 seats, but only if the flimsiness doesn’t matter.