It was interesting to see both versions side by side. I have used one of these versions, probably the 2010 version in my lecturing when looking at mobile robots. We looked at sensor systems for positioning and movements as well as different coordinate systems. I had 20 of them. I would run a class of up to 40 students working in pairs with a sequence of measurements on repeatability and accuracy. It could get pretty noisy and confusing when all 20 Bi-Traks were running about beeping as well as flashing. When I left I locked them all in a cupboard and for all I know they might still be there!
I can also remember looking at the 6 D cell version and worked out that it was using a the 6 x 1.5 batteries to make a plus/minus 4.% V supply so that half bridges could be used to drive the motors backwards and forwards. The new version used only 3 cells to make a plus 4.5V supply and must therefore have used a full H bridge drive for te DC motors.
I also had a student work on a project to replace the keypad with a PIC microprocessor creating the equivalent of the button presses so that by adding a Bluetooth communications link (HC06 I think), a remote programming system could be created. It did use a matrix approach to the keypad but seemed to be some sort of weird voltage level, only about 1.2V so it could have used something like resistance to detect the key presses, or maybe currents, instead of voltages. We never did get it sorted and working.
I miss my Big-Traks. I did look into buying my own when I retired but the second hand ones were all a bit dodgy looking and were still quite expensive. The company also made a smaller version shortly after the larger Big-Trak version, which was a bit annoying as the larger size versions are pretty big and 20 of them took up a lot of space. The smaller ones would have been much more convenient.