I agree that they are expensive for what they are.
I researched some other options before and Lii-MP2 reportedly has conversion efficiency below 70% which ain’t great.
Can’t confirm that, but here is the sauce (I used YT translation): https://www.youtube.com/watch?v=RMgqub_ww9Y
I do not think that I will try ordering the 4th time anytime soon.
I spent too much time researching, waiting for them to arrive and then returning.
I own good (balance) chargers and lab equipment (multimeters, lab power supply) and quite knowledgeable about Li-Ion, Li-Po technology. Just wanted to reuse 18650 cells in the powerbank as I deem those safer than flat powerbanks that became spicypillows after a while.