It's correct, that flight times won't be long - that's the downside of it!
Don't compare Apples and Oranges
But Paul (the creator of this project) is not claiming to build an electrical paramotor that is supposed to compete with a 2-stroke paramotor.
He is saying himself that it is supposed to be an affordable, lightweight and small (foldable) solution for pilots who aim to be able to get in the air for 20 minutes or so, after work.
I personally own and fly a gas powered paramotor. If the tank is full, I can fly for 3 hours or even a little longer. However it's loud, lots of vibration during flight, easy engine out when it runs idle for some time in the air (while thermalling for example), it's large and big to transport (unless I want to disassemble it every time, which I don't want to) and it appears that I will need to make sure to keep it well maintained (I have only flown 15 hours or so with it, since I own it)
Advantages of Paul's project
Paul's project however has tons of advantages, if you accept that it will only run for 20 to 60 minutes, depending on how many batteries you want to carry:
no vibration
maintenance free
less noise during operation
unlikely to fail (engine out)
easy to start at the push of a button (I agree, this is also true for electrical start gas motors)
folds up in seconds
lightweight (unless you want to carry lots of batteries for longer flights)
Plus: there are major companies and laboratories working on improving battery technology (think of Tesla alone) which will definitely result in battery technology to become much better (higher energy density) in the near future.
