Adult birds can eat it but it won't do much grinding.Interesting. It says Chick Grit but on the back it also says "suitable for adult birds".
Chick grit is about 1/16", #2 grit is about 3/16" and suitable for up to 6-7 weeks.
Adult grit is #3 size and is about 5/16".
You do know chicks don't need treats and treats are supplanting the optimal nutrition in the feed.
They can find grit when foraging depending on what is available on the ground.