Is it just down to layout?
Yep. How it looks on screen, as well as navigating the steps needed to perform various actions. But as already noted, either of these, or Win500, can handle your programming.
A number of people on RadioReference have one or more ARC programs (from Butel) for other scanners, and prefer the 'look and feel' of the ARC software. So, those are often inclined to lean to ARC500. I have all three programs.
Use the free trial periods, then decide which one you prefer.