To use USB OTG feature you need few things like OTG cable or OTG Pendrives and then plug that into the charging port of the phone and you will be able to see all the files on that pendrive in you My Files app.You can connect your external hard drives to the phone and the view the files stored on those drives on your device.
You can also check the specs here: J5 Prime specs
Samsung Galaxy J5 Prime vs Vivo V5
Both the phones have their pros and cons, but I think you should go for Vivo V5.
Vivo V5 has the following advantages over Samsung Galaxy J5 Prime:-
1. Vivo V5 has 3000mAh battery while Samsung Galaxy J5 Prime has 2400mAh battery.
2.Vivo V5 has 20MP(Front) Camera while Samsung GalaxyJ5 Prime has 5MP(Front) Camera.
3. Vivo V5 has 5.5" Display Size while Samsung Galaxy J5 Prime has 5.5" Display Size.
Samsung Galaxy J5 Prime has the following Advantages also:-
1. The Weight of Samsung Galaxy J5 Prime is 143 grams while Vivo V5 has 154 grams weight.
Verdict- In my opinion, Vivo V5 is a better phone in overall performance but if you need a light weight phone than you can go for Samsung Galaxy J5 Prime.
You can also see the comparison between the devices on 91mobiles: Samsung Galaxy J5 Prime vs Vivo V5
LG Stylus 2 vs Samsung Galaxy J5 Prime
Both the phones have their pros and cons,lets analize both:-
Advantages of Samsung Galaxy J5 Prime
1.Has Dual Sim:-Can multiple sims at the same time.
2.Faster CPU:-Faster CPU means more smooth experience.
3.Has Fingerprint Sensor:-It allows you to quickly unlock your device using your fingerprint.
LG Stylus 2 has the following advantages -
1.Bigger Screen:-more pleasing experience on a bigger screen.
2.Slimmer:-Slimmer devices are easier to carry
3.Bigger Battery:-So it can generally last more time.
4.Supports NFC:You can also connect two NFC enabled devices just by touching them with each other.
Verdict - In my opinion, Samsung Galaxy J5 Prime is better overall performance and price ,if you need Slim handset and better battery life than go for LG Stylus 2
You can also compare these devices on 91mobiles