Yes, Realme 1 supports OTG. USB OTG or USB On-The-Go is one of the most recent technologies that allows you to connect your pen drives and in some cases hard disks to your smartphones and tablets. It has a cable and through that cable, you can directly view and use your pen drive in your smartphones.
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You can also check the complete specs here: Realme 1
Yes, Realme 1 supports VoLTE in both the SIM slot but there is one catch that you cannot use both the SIM on VoLTE at the same time ..If SIM 1 is on VoLTE then the other SIM will be on 3G network.
Check the complete specs here :- Realme 1
I will recommend you Realme 1. It comes with 6-inch IPS LCD display which exhibits a screen resolution of 1,080 x 2,160 pixels. Under the hood is a MediaTek Helio P60 assisted by 6GB RAM which gives the best performance in the class. The camera setup consists of a 13MP primary camera which can capture very nice images along with an 8MP front snapper.
The RealMe 1 is a great smartphone which comes with a lot of strong features.
You can also check the complete comparison here: RealMe 1 vs Xiaomi Redmi 5