I've been using the same Givi cases on a lot of different bikes, as both side cases and top cases, and given them a hard life. See the map in my sig? They've been everywhere, and overloaded too. They have outlasted several motorcycles. They have always been waterproof, and never given me any trouble like people get from the NT's integrated luggage. It's been nice to be able to order key sets to key them alike, and new racks to put three cases on the bikes that didn't have integrated sidecases. I loaned my cases to one of my girlfriends, who crashed and slid her bike down the road on one of my Givi cases. After the accident, the case was scratched but still perfectly serviceable. I ordered a replacement lid a year or two later, just for cosmetics, and the price was reasonable. The JCW top cases are probably fine, but I have liked the availability of Givi spare parts and additional pieces as needed to fit later bikes. And after the great service life I've had from my Givi luggage, I feel I've had my money's worth and expect to continue having my money's worth. I'll have these cases long after the NT is gone.
Now the E55 Maxia case I've put on the NT, that was basically a silly purchase - I didn't need it, I could just keep using the cases I already had. But I just wanted it, that magpie urge y'know, the shiny it calls to me.
But I wouldn't have bought it if I didn't already have such a high opinion of the Givi stuff.
But if I were just looking for a topcase, cheap, I might go for the JCW case too. Not sure I'd feel comfortable with it as a side case, though.