Hey - how does all this affect us that "don't" have O2 sensors

I could go to one our local shops with dyno's but I have not talked to anyone that has been impressed yet. Was told by one dealer it would be 3-400 for a dyno tune and they would give me a copy of the SERT MAP.
Or I could got the TwinScan II+ route. The kit seems as though it works similar to the MasterTune, log data upload cut & paste download etc. The TwinScan II+ includes the necessary O2 sensors, data logger and O2 interface.
I am considering this route as I have new pipes coming that are ready for O2 sensors, so this seems to make the most sense.
What is the difference between MasterTune and TwinScan?
And from what I am gathering here - AFR's are setting our desired AFR across the board or is the tuner setting the AFR.
If it is user set how do you know you are setting the desired AFR correctly?