As you all point it out alreadly.
Supercard Hardware is more complex. The M3/R4 uses a single chip solution, from the PCB traces, most of them route directly to the IC I/O. It seems that they had got a more efficent way to decrypt & send data from the flash. Thinks this way, if stuff can be done in a single chip solution, why run the hassles of using two chips and transmit data in between them.
Second, the battery. If the cart rely the uses of a battery, thats means your battery will eventually run out. You then have maintance hassle for battery replacement.
Third, the 2 chips solution to me will drain more battery power to the stright forward 1 chip solution.
Fourth, the mechnical PCB layout, M3/R4 had a small curve design for the ease of taking in/out the micro sd.
Lastly, more component add up to more cost. More labour cost for mounting the component. The reason why supercard is more expensive then M3/R4.