I had Anker 21W panel before and get this one as an upgrade since it has twice wattage. My main reason for upgrade was that I mostly don't have direct soon in the bush, so 40W panel theoretically should give me more power than 20W one when in shadow. I use it for camping trips, and it charges phones and power banks. I didn't run all detailed tests, just measured it with cheap USB meter - but in full sun it gives me 2A for USB A port. I measured USB-C with my phone and I got over 2A. When this panel is in shadow it still produce electricity, at least power banks are charging but I guess not as fast. The only improvement it need in my opinion is a pocket to keep cables and protect controller, so I glued piece of plastic at the back of the panel to keep controller off the ground and store usb cables.