I have an Anker 20100 mAh PowerCore in regular use since 2016, and i never had an issue. The only issue is… that is too heavy for EDC.
Weight apart, it’s the only item i tried that really can perform 5 or 6 full-capacity recharge of my cellphone (i.e. an entire “stand alone” week of use).
Last time i have tried to see if the storage performances were still good i put up a 6 LED USB stick on it… ended that i took it off after 3 days of continuos use, and the battery capacity was still over 50%.
That said, i think that everyone has his own history and experience, when it comes to tech&gadgets… the good thing is that we share it here with others ! 🙂