Suit youself. But this code does not really build a custom GUI control. Rather it simply changes the type property on the input from "text" to "range" which is a standard feature of HTML5 and availabe for years in all modern browsers.
If you look at this problem in isolation you might come to the conclusion it is "twiddly" as you say. But when you look at the problem of missing features in QuickBase more holistically you will find that there are many more problems that can be solved with a tiny amount of script in a similar fashion. So from my perspective it is worth solving every problem with script for which there is no native feature hardcoded into the product.
Just don't accept the excuse that it can' be done natively or quite frankly that such-and-such a feature isn't in the product development pipeline. All the Web technologies have matured enormously from the time when you formed the opinion that asking for changes and enhancements have to go through committees and are risky and costly to implement.
