It is not a simple count
I used David, a version of this computer, in 1980-1981. I was on a team that was managed by Steven Goldberg and financed by Tommy Hyland and his group. Tommy brought me in to the group. We were friends from college, I knew how to play blackjack and count, I am a computer programmer, and he trusted me. I met Steven in Las Angeles to see David first. It seemed to work as advertised.
After actaully joining the group, I had the opportunity to work with a support person that downloaded the program so that he and I could actually look at it. It is in machine language and so not many people would have any idea what to do with it, and it would not work on a regular PC. However, the program actually has registers that keep track of how many of each value card are left in the deck. When you take out all the cards that you have seen so far from the shoe, then enter your cards and the dealer up card and tell the computer to "play", it runs through every possible combination of cards left in the deck and determines the best play based on the rules set that has been selected. So there are clearly times that it would do things that no count system would tell you to do.
At the time that I used the computer, it was legal in Nevada. None of the people in my team was ever arrested, and only one person was ever questioned. However, some of us took computers to Reno and played as a second small team. A woman that was an operator was back-roomed but they never actually searched her, so they did not find the computer.