I’ve not come across double happiness, but have used Double Coin and Kormoran quite a bit on trailers, and once on a steer axle as it was all the fitters had available at a roadside breakdown. They have been reliable and given reasonable wear at the price. They’re absolutely fine on the sleep and twisty roads I operate on, and if you are unlucky enough to take one out on a hidden hazard, it’s a bit less painful on the pocket.
Not sure that they would compare so well on high mileage, high speed work though. As ever, it’s horses for courses.
(I use GITI also and find them fine)