As it has been mentioned previously, the casters do leave more to be desired. Even at that, it wouldn't be a problem to by some new casters and resolve that concern. With a set of RWM 47 series 6" casters you'd be able to up the capacity to 6,000 lbs, dependent on wheel material. That should be more than plenty.
Another concern is the price point. I feel that they made a good choice of what level of quality and price point to aim for. The market for low end consumer to budget prosumer tool boxes is flooded with options. On the other hand, the professional/industrial grade market doesn't have nearly as many options. Sure you can buy a used box for a steal of a deal of you keep your eyes out for a long time, but it will still be a used box and may or may not be similar in build quality to the Tekton. One standout feature of the Tekton boxes, as well as other industrial grade boxes, is the drawer slide design. Ball bearing drawer slides are nice and can be heavy duty, but the carriage style drawer slides put the ball bearing ones to shame. They are so much more solid and have far less deflection than any ball bearing slide I've come across. Also the load rating is 400 lbs working load rating, not max. If you look at Accuride slides (ie Snap-on KRL & EPIC) they are rated based on the weight, number of cycles, and the width of the drawer. If you run Accuride slides at the max working load, the cycle rating is significantly less than if it were at 50% capacity. This isn't to say that ball bearing slides aren't good, I'm just saying that the carriage system that industrial grade boxes use is better. Also, I'd imagine that the build quality is every bit as good if not better in some aspects as top of the line tool truck box. So, once you start to compare apples to apples the price of these boxes become much more reasonable. Branding aside, I'd assume based on my experience with other industrial brand boxes I wouldn't hesitate to pick the Tekton over a conventional style tool truck box. This is why the price is high, it's an industrial grade box that's made in Canada with premium build quality and construction. This is why I'm interested in the Tekton boxes since I feel the value is there and it's backed by a solid company and manufacturer.