I have a 14 gal Chronical, had the extensions, and got rid of them, mainly because they make the Chronical way too top heavy. It took just one mistake (moving the Chronical when the casters stopped on something) and down she went. No loss of beer, but a nice dent in the side to remind me of that moment. So I removed the legs, bought the Heavy Duty Casters, and have never missed them. That was about two years and 40 batches ago and no problems with my beer, and no problems with the stability of the Chronical.
(BTW, the SS Brewtech HD Casters are absolutely worth it, especially compared to the cheap casters you would get at a local box store.)