1. It's dirt cheap than any other solution I found($15, I use 10k mah version)
2. I can plug RPi to it and I can plugin a charger in 2i. When the main power cuts off, It'll instantly switch over to battery with 0 downtime. I think this is called passthrough charging)
3. It can provide 2.5 or 3.5 amps(not sure about exact value) output
4. It has two ports
This alone is a killer feature that’s far less common than I expected before I started searching for it. Most power banks cut off output while they’re charging, and many require physically re-plugging the device to start powering it again.
I ended up acquiring a PiJuice for this functionality alone.
Edit: Someone linked pijuice project. I went to their website and according to them, Their 10k mah version lasts 24+ hours
> Onboard 1820 mAh off the shelf Lipo / LiIon battery for ~4 to 6 hours in constant use! (with support for larger Lipo Battery of 5000 or 10,000 mAH+ to last up to 24 hrs +)
https://uk.pi-supply.com/products/pijuice-standard
So, I would say 2i would probably last about the same?