They're not just tests. They're training. You will learn things from the process that would take a long time to teach you just learning things shop by shop.
It's like the difference between stumbling around on your own trying to learn to use Quickbooks versus taking a class at the community college and learning to use it in a few hours. On your own, you'll learn to do the things most important to you but in a class you will learn about features you never thought to look for. Training may teach you skills to help you in shops you haven't yet tried or were afraid to try.
Having been through both of them at this point, I can say they can be of use to newer shoppers and a good refresher for former shoppers who return to it, but not much actual value to long-term, currently active shoppers.
Unless the schedulers do give preference to the people with certifications, which many say they do.
I expect I'll get my money's worth out of it in the long run.
Time to build a bigger bridge.