Yeah I would not expect much out of the inverter, and it's also not pure sine wave. I think the idea is you can plug stuff that does not have a USB adapter, so like maybe camera chargers and such.
I actually built my own system a while back for camping, it's much bulkier though, uses 14ah of lead acid batteries and has a 60w foldable solar panel. Absolutely not something you'd backpack with, but handy to have in the tent for lights and stuff. Was even able to power the air mattress pump.