So I have this power bank for quite some time and it works amazingly while I'm at work or on the go for school or at school whenever I can't find an outlet, and so far it works great for an alternative. I even let friends and co workers chime in on using this and it's always funny to see them react to this big brick of electricity. On the segment on charging power bank it does take a bit of course and it's nice that they give you a 45W wall charger alongside it for optimal charging, but luckily I have a 60W so I'm quite happy of having 30 minutes less of charging this thing lol.
Of course as the title says there is a little note I want to give, I been seeing a lot of reviews of people complaining that the charger is not of actual charging capacity as its advertised and I want to help clear up the misunderstanding that they and/or you have. Whenever it comes to charging a device, and this can go for any powerbank, there will always be a power loss on charging devices, meaning whenever you do charge your laptop or phone or whatever, there is resistance between the bank and the charging device giving a portion of the energy transferred "lossed" and thus makes charging little less efficient as people would expect them to perform, about 5-10% less than what you would expect
TL;DR- Battery is good, buy if you want. Because we don't live in a perfect world and its a battery, it's not 100% efficient as you would expect.