We only like it for 2 reasons:
1) It is a neccessity
2) There is no better design available yet
Good:
It works, and works well. Holds a few carts, an atom/cart combined, and charges an extra battery. 510 batts die fairly quickly, so you must own a PCC if you ever leave your house.
Bad:
Hinge pin slides out all the time, you have to keep an eye on it and push it back in before it falls out and gets lost.
Sharp edges/corners. Not good for carrying in a pocket often.
If you don't keep an eye out on your LED, the PCC will drain your battery after it charges it. It will drain it totally. The only way around it is to watch for the LED to go out, then flip the battery. Of course the flipped batt doesn't fit well, it is a really tight fit, so the next time you open it... REMEMBER you flipped the bat, and hold the lid. Otherwise... PATOOOEY! The batt flies across the room.
Silly design as far as the odd shape and size. Had they made it wider and a hair longer (like a pack of 100's) it could hold more carts, and could carry an assembled 510. As it is designed, it is not too practical. You have to carry the PCC and still carry your 510 separately. If I could meet the genius who designed this thing, I would shake him... violently.
Someday we'll see a more practical, functional PCC offered (I hope) that will do a better job. There is one on the way for M401's, so there is hope for the 510 at some point I think. Until then, we must be content with the current PCC.