Good. Great. Easy. Promos, quality, warranty, speed of delivery. Of course it's also a marketplace and there are different sellers with different goods and service quality. But You can always see reviews and be sure GearBest will support You in case of something.
As for orders from GearBest. It's the best. Always fast delivery, good packaging, original and usually international versions of devices. And many branded deals.
Application requires some work and they always glad to receive users reports and improve functionality. Support is always in touch.