I love the size, it has plenty of power and capacity, but still portable enough to just toss in the car and take with me.
I noticed if I leave a large 240w solar panels connected, it gets into a weird state as the sun rises and will not begin charging on its own, I have to disconnect and reconnect the panels well after sunrise and the voltage is higher. Which means I loose several hours of charging time each day, or an entire day if I am away for the day...
Other than those things, I love the 757. It's small, powerful, easy to use, and has LiFePo4 batteries that will last thousands of recharges longed the other lithium battery types.
I wish the solar charger could take more the 300w and higher max input voltage, but that is well documented and I knew those limits before I bought it.