I travel and I go through battery banks like crazy, I have a tendancy to drop them. For the price, this is a nice unit. It has the 20000mAh power so it will charge my phone several times. I usually leave my phone and tablet plugged in when I have long flights so I can watch movies with no worries about arriving with a dead battery.
Like the others that are similar, it does take a while to fully charge (overnight if not longer if it's completely drained), but it does hold it's charge in between charges. It's a little heavy and bulky... but all are in this size/capacity.
Overall it's cheaper than most that are similar and it does an effective job. It also allows a thru charge... so you can plug this into the wall and charge multiple devices using it's "out" ports.