The price, I'm not doubting its quality. I can't speak to that
Edit: So what COULD be happening is someone saw the deal on banggood or somewhere else and approached Drop to offer this pair of products. This would essentially be an unnecessary middleman that would be profiting off of the sale he/she found. It could be argued that finding the sale and coordinating the deal with Drop is a legitimate service that is worth the extra cost, but in my opinion Drop should be the only middleman in the products it offers.
What also could be happening is whomever is actually producing these products IS working directly with Drop and the sale on banggood is just something banggood is doing as a promotion.
We really can't know what is going on behind the scenes, but as it stands Drop's deal is simply inferior at the moment