Wait for someone to have a shower. Check that all your connections are secure. Then check your gutter. Check that the water spurts along the gutter are going into the sunken pots. If not, move the gutter back or forwards. Does the gutter need raising in certain areas to make sure that the whole length fills? Mine did. I never had to bend up the end of the gutter near the outflow as it is slightly higher than the far end. If the gutter is reasonably level with just a little fall, then each sunken pot should fill with about the same amount of water. If you decided to use this shower watering system without the sunken pots you would lose the visual cue of checking on each pot to ensure that water distribution is fairly even.
Then enjoy. It's really fun to go out into the garden while someone's having a shower and watch all that water being put to good use. Sounds like a babbling brook too. Very peaceful.