I know there are a few of those VR box things that you put your smart phone into to turn it into VR.   (like ~$20)

Curious, to get opitions on those that have done this and their feelings on using it.

Yes you will lose all DJI GO app functions during fliight, as your phone is in your headset - but does it practicly work for FPV?

Mine works great.  I use it with my Samsung Galaxy S5.

I use one of the cheap goggle sets. As you say you lose a lot of app functions but for straight flying they are great. FPV with goggles isn't quite as immersive as I expected but I had a lot of trouble eliminating the glare from my phone and iPad, even with a hood, and the goggles fix that completely. Make sure you get a pair that lets you adjust the lens 2 ways so you can adjust it to suit you perfectly. If you need reading glasses you might need to wear them with the goggles so make sure the pair you choose can be worn with glasses.   

The funny thing is that litchi app is more expensive than vr glasses.. 25usd vs 20usd ;D

I bought the VR box. They work great . Definitely cures the glare problem.