Not bad, but needs direct sunlight if possible.

Full sun on unregulated Port: good 0.4A @ 5,7V -> approx 2.5W
This is considerably less than the manufacturer promises, but realistic values ​​appear to be generally uncommon in the industry. :)
At Port regulated the voltage remains closer to 5V, the current goes back even minimal.

Of arrive at simple USB chargers in battery about 0.15A, ie a micro-battery would be fully in one day, a Mignon would need at least 2 days. 2 at the same time are battery's a little more than one, but only insignificantly in the sum.
(I tested 2 different USB chargers,

Shade or cloudy come in the same charger to approximately 50mA = 0.05A, so would need a micro-battery has at least 2 days for full Will, a Mignon about 4 days.

So you see, although it works, but if you do not want to have too much patience, one has to rely on "real" sunshine.
So rather nothing for English weather ... :)

The feel and quality make the external appearance the way a duchaus good impression.