It would be hard to root prune in a pot. That's usually done in the ground with a shovel to keep runners under control. The problem with using the pot you describe is that the bamboo will send rhizomes out and they will circle the pot, and form a pretty dense rot ball with a diameter larger than the top opening. When it comes time to repot, the only way to get it out may be with a hammer (to smash the pot). I only plant bamboo in pots that taper outward at the top. I recently helped a friend get a bamboo out of a wooden container with nearly straight sides, and we half destroyed that.

One other thing. With any potted bamboo, it helps if you line the sides of the pot with heavy duty plastic. This has two benefits: it reduces moisture loss of the pot, and it makes it easier to remove the root ball when you need to do this.