No, I only let DD2 ride without it in the van if she's sitting in that Plus One seat. She has to use a booster otherwise. She doesn't complain, but every now and then she'll sit in there without a booster and ask me if it looks like she's big enough to ride without one
I know it's on their minds since none of their friends are in boosters, and haven't been for some time now! When they do ask about it (which really isn't often), I just remind them of the 5-step test. It's extra hard because they're twins, but they are so different in height so DD2 is gonna 5-step it waaaaay before DD1. Fortunately DD1 is my easy child but I kinda feel bad for her