I've heard reasonable about Powerextra batts ...
I think one of the problems is that eg Amazon .... Despite their claim to be 'whiter than white' - they are not. There are many examples of clone / rubbish items of all sorts sold by Amazon sellers. People forget that in reality Amazon are really just a fancy eBay style outlet.
Second that any 3rd party seller cannot always g'tee stock from same source. That's why you see one person saying their P3 battery has the Y shaped LED's while another says they have the normal I shaped LED's from same seller.
I also think that many people who buy 3rd party batterys are shy of posting they do because of the typical backlash that gets posted about falling from the sky etc. (Total rubbish by the way - I don't believe it. I've been crashing and causing mayhem on RC fields for over 50 years and its as rare as Rocking Horse **** to know exactly why a crash occurs unless its a mid-air or you switch of radio !! Too often I have said what caused crash on the field but then when I analyse the vids - find its something else.)
There are claims that DJI FW detects non original batterys ... again thats rare .. so rare in fact - I do not count it. I accept that a real poor copy may do that ... but for most I don't think it would happen.
Lets be honest - reverse engineering a smart board is not hard for a suitably equipped factory to do ... and also Chinese factorys are not averse to running two lines ... OEM and another !!
Personally I would decide on a reasonably priced budget 3rd party and give it a try. But that's me !!