There's not much point in pairing two iOS devices. You can't share files that way. About the only thing you can do is use it to tether one device's internet to the other. Something that works far better using the hotspot feature. Bluetooth tethering is a legacy method for older iPhone models that can not create a hotspot. On a stock iPhone both the hotspot and Bluetooth tethering have to be enabled by the carrier.
Apps that use Bluetooth to communicate or transfer files between two iOS devices do not need or require pairing through Settings. They handle discovery and other functions directly in the app.
Since you mentioned jailbreak, I believe there a a couple things you can do via bluetooth pairing that can not be done on a stock device, but I'm not familiar with them. You would have to ask the folks here that do jailbreak. They hang out in the Hacking area of the forum.
Once upon a time I did pair my iPhone and iPad, just to see what would happen. It took several tries, with a lot of turning Bluetooth on and off again, to get both devices into discovery mode. Once paired, nothing special could be done with it, beyond the internet tethering already mentioned.