You could tape the sides, then if you want to see the roots, just lift the plant and look at the bottom. Best of both worlds. Plus some people believe it's nearly impossible to get root bound. And I'm starting to believe them having seen 5' plants in 32oz cups. The main thing is deeper the better, which sucks in small head room spaces, and just making sure it's getting enough oxygen. Too wet and it can't breath, but you don't look like your having any problem with that.