For what you want to do, either bike will suit your needs. Rollerbrakes are generally heavier than other bike brakes. This is one reason they are less common on many bikes, where weight can reduce speed and becomes a deterrent for more serious bikers. Given that you'll be riding with kids on mostly flat surfaces or easy rolling hills you probably won't notice the weight difference. Having said all that, there is a definite difference in style between the two bikes which will translate into comfort for you. This difference is rider dependent so I'd go with the one you find easier and more comfortable to ride.
On a purely personal - non-technical - level, the GUSTN looks like the more expensive bike while the Gotham may be the better value.
Last edited by Tony P.; 05-01-20 at 09:54 AM.