3gb RAM, 32 gb internal memory, 4100 mAh battery, super attractive UI. Pick up any phone available in the market with these features, its minimum cost would be 12-15k. Redmi 3s prime in that case, costs only 9k. Apart from that, the screen size is 5.0 only, which is a great advantage for one handed users. One plus-x is the only another phone available in the market with 5.0 display. The only drawback of 3s prime is that its display is not full hd, which doesnt differ much for a small screen size.
I bought 3s prime last October and it is still running smoothly. The battery life has gone a little shorter than it initially was. But still it will run for a day easily.
I admit it doesnt have a full hd display, high pixel density or a very fast processor or a turbo charger. But dont forget the price is only 9k ( even one rupee less) . I can guarantee this one is the best in this price range.