If it's anything like the Cybook Gen3 (another Netronix clone), the SD card is a little tetchy, yes. You have to push very hard until the card is a little lower than the edge of the card slot and wait for the very obvious click to know that it is home. To get it out, you have to push it DOWN and it should pop out then, enough to pull it out.
It works, absolutely, and I've had my Cybook nearly two years without a problem. I keep all my books on the SD card, so I'm always popping the card in and out to load new books. It hasn't worn out. I don't know if the mechanism is smoother, or maybe I just got used to it.
Also, you insert the SD card with the top facing the back, which to me seems backwards.