The pebble is pleasing to hold and behold, being small, attractive and with a lovely smooth but tactile finish. Electrically it works extremely well. It is quick both in storing and releasing charge. One star off due to outdated plug/socket types with regard to mobile phones; surely the largest market for the pebble.
The socket receiving mains charge on the pebble is the old concentric Nokia style. The supplied cable has a full size USB plug on one end, with the other end being a plug to match the charging socket. This allows the pebble to be charged from any USB socket and the cable takes adapters for micro USB, and various bespoke plug types, including Apple. If you lose the cable or the adapter for your phone, the pebble becomes a paperweight.
Given that the mobile phone industry has standardised on the micro USB for charging, it would have been ideal if the pebble had had a micro USB charging socket. This would have allowed the vast majority to use the pebble without any extra cables, since they already have a USB to micro USB for charging and data connection. The converters could then be from micro USB to bespoke connector, incidentally allowing owners of non-standard phones to use a standard charging cable.
I hope that a future model will switch from the old de-facto Nokia connector to the new micro USB standard.