That sensor seems to be very far forward compared to the driving wheels -- even a small amount of difference in rotation will turn the front very far. Did you consider putting the sensor between the two big wheels, and driving the robot the other way (dragging the ball behind it)?
It's funny that the standards scam comes from those who have lobbied to outsource testing to private interests. If standards are government produced, FOIA means they would be free!
Codes come from the time when unsafe businesses burned down entire blocks. This still happens in places like China. If all US businesses had the integrity of pololu.com then all these rules wouldn't be needed for public safety. But history shows it only takes one corrupt utility to poison an entire city. ..
You might also consider that distributor sites that professionals rely on every day, such as digikey.com or mouser.com, do not have product comments. What they do have is good parametric search, which is something that your site now also has.
Another commonality between you and Digi-key is that what you sell, requires skills and research to use, is well documented, and works as documented. On Amazon or Newegg: not so much!
Btw: I think you allow open discussion in your forums. Good enough for me! A link to the appropriate forum section for each product would be icing.