The shape is a bit different, but both boards work as intended. Both have LEDs, but the Gravitech LED is on whenever a card is inserted (I think using the socket’s mechanical card detect switch) and the Adafruit LED blinks while data is transferred to/from the card, which I think is the more useful function. Both have “push/push” type sockets (to release card, push in, it clicks and springs back out). They are from different vendors; the Gravitech sockets seemed to have a bit more friction and were more sticky overall, and tend to grab on to the cards rather than release them cleanly, but they seem to improve a bit after a few cycles.
Via the forum.