It is possible that there's some physical defect. The SD slots are delicate slots. Best to handle them with care and in case of the double slot carefully see where you put the SD card because it's possible to put it between both slots.
The operation of the cart is not buggy at all. Sorry to exclamate so fiercly, but it's just the way it is. It can be overwhelming because Guillian has carefully anticipated for solutions for all situations you can think of. That gives the user a lot of options. But in normal use only a few options are necessary to operate with the cart without any problem.
There are other devices which you could think of to replace this cartridge, but you won't get any better than this one. I am no personal friend of Guillian and I do not have shares in his business. It's just the way it is. Other cartridges lack options which this one has or are way more complex in use. Since Guillian is one of founders (if not the) of this concept many years ago he has a lot of knowledge and experience about it. If I'm not mistaken the system that runs on it (Nextor) was written to be used by this cartridge and was later adopted by other manufacturers. It really is top of the line.
I would like to record a video of how I use it and post it here. Then you compare it to how you use it. If you're doing the same as I do, think of an RMA and replace it. It's in Guillian's best interest to provide you with a proper device as well. It's his good name that's at stake.
Another thing about the shipping. It's quite normal use to send it in a bubble envelope. A box with loads of foam won't protect it any more than the envelope already does. It's sturdy stuff. If anything brakes it in the envelope, it brakes is in a box with foam as well. I've received about all my cartridges this way. Even without the packaging that goes with the cartridge. It just doesn't brake from a bit of throwing around during shipping or being dropped through your mailbox.
But first let's see if you use the cartridge as intended and deescalate this topic. I'm confident everything will turn out for the best for everyone involved 
