Haven't got one myself but I'm guessing:
Slightly poorer efficiency spinning due to thicker, less efficient hub profile to wrap around pivot points. Great pumping and surfing as it's only when it's not running that it would fold to reduce drag and equirement to match water speed with prop speed.
For people with no near surf or easily foilable waves, no point as you'll always be spinning it.
For waves I'd think it's essential !
And if you want to double up and take a hand wing as well, you'd want it to fold.
Disclaimer- Not sure how well the board responds to pumping but I have a feeling from Chinese stuff I've seen on the web that batterys are usually close to mast so pumping should be easy. For anyone wanting to practise pumping a foil, perfect! Power to speed, cut motor, pump till tired. Boost to speed, repeat. I can't see that being nearly so practical with a rigid prop.