How long does it last on a full charge?
It depends on the size of the inflatable item, as seen in the linked video, it can fill a swim ring, outdoor camping mattress with a water mattress no problem;
Is this air pump for inflating things bulky or lightweight?
This USB inflatable pump is very lightweight and easy to carry, mainly designed for outdoor play to inflate camping mattresses or water kayaks;
Can this USB air pump be used to inflate balloons?
This air mattress inflator pump does not support inflating ball and tire type items;
This little unit have any other function besides inflating?
This is diminuative in size, easy to operate and has a long battery life, it would be very useful at the beach/river blowing up all those plastic toys you take with you. Removal of the air would be a snap!