Well, you don't "have" to buy the filler but, yes, it will be a much cleaner look. Don't get me wrong, the custom job isn't that bad for for all that work with fiberglass, the JDM console will still be cheaper and better looking IMO.
I've heard that Tater (from this site) might be doing anothe run of his carbon fiber nav-fillers for the JDM console. You can also find them on the "other" Celica site apparently. The M770 looks great with the JDM console and I agree that the buttons look a little sketchy on the other model. You could get any screen you want as long as it fit. Those Alpine ones are really just the best example.