Your smart devices will treat Pokefi WiFi a normal WiFi network, therefore you will no in data safe mode while using the Pokefi.
This means the Pokefi will use more data than in cellular data network.
In particular, so-called streaming services such as YouTube will deliver in higher quality if you are on WiFi network including pocket WiFi. For example (refer to the screen captures), a 33 seconds SmartGo video will use ~5MB data using 4G, it will increase to ~11MB using WiFi. The longer the video the bigger the differences. It could be up to 32 times more in data usage for HD video using WiFi network.
Sometimes you have the feeling of data goes away too fast than expected without knowing why.
See below for useful tips to prevent unintentional data use.
Tip 3 - Make sure you have turned off automatic backup for Instance Message Apps, such as WhatsApp.
Tip 4 - 'streaming' services such as Netflix, Spotify and YouTube might use large amounts of data. This also applies to video and audio files on Facebook and other social media.
Tip 2 - Make sure you have turned off cloud drive auto-sync, such as iCould,Dropbox, One Drive etc.
Tip 1 - Make sure you have turned off automatic download, such as Apps, Music and software updates.
There are many Data Monitor apps available you can use to check data usage by yourself.