The Ultrax (Gens/Tattu) batteries are not higher capacity than stock H batteries. The Ultrax batteries are just labeled correctly. The stock Yuneec battery is mislabeled with a capacity lower than they actually are. There has been no admission or explanation for this, but we might presume that mislabeling the battery with a lower capacity will permit the maker to transport more batteries in a single shipment after the International (IATA) Air Transport Association placed higher restrictions (reducing the the number allowed in a single air cargo shipment of higher capacity batteries) on the shipping of lithium polymer batteries. Yuneec previously did exactly the same thing with their Chroma batteries. Several other battery manufacturers have been slipping a second label with a lower capacity value over the correctly stated label on some of their products.
The flight time you will obtain with the Ultrax batteries is generally the same as with factory Yuneec batteries. You just pay a lot less for the Ultrax batteries. They are very good batteries.