As oneplus one and mi 4 comes with almost same spec but mi 4 goes ahead in most of the department like call clarity, camera and it have optical image stabilisation which is absent in OPO, stable operatinig system as compare to cynogen in OPO, GOOD after sales service which is a big issue with OPO and there is no yellow tint in mi 4 as there in OPO. there are some addition features which mi 4 offer like auto call record system is inbuilt you donot have to download any third party app.
Its single hand gesture, security feature like virus scan, clear cache memory is inbuilt, its price is still less then OPO, battery life in mi4 is much much better then OPO and MAINLY YOU DO NOT REQUIRE SILLY INVITE TO BUY MI 4 as this is require in case of OPO. so just go and buy it:)