I pick rustoleum for off the shelf/find anywhere reasons, IME it goes on better looks deeper and polishes up way better than duplicolor. There's also Krylon and VHT to try too but I don't have much experience with them besides satin with the former(which works great for interior pieces). There's much better rattlecan clears that can be bought online, for a price naturally
It'll mix as long you're not putting Lacquer over Enamal, which is a combo that will ruin the paint. Otherwise I mix and match brands all the time with no issues, I did my license plate frame with Duplicolor adhesion promoter, Krylon primer, Duplicolor performance white, Testors gloss pearl hobby paint and topped it off with rustoleum clearcoat and it looks better than half the real paint on the car.