Today I bled the disgusting 10 year old brake fluid out of my dad's vehicle with a little pneumatic tool that sucks the fluid out nicely and started with rear right, rear left, front right, then front left making sure the reservoir was always topped up. I used dot 4 synthetic.
I test drove the car and it felt good. The braking felt smoother to me and overall just better. Then I had my dad test it and says 'dude you got air in the lines' and it feels too soft for him although the pedal never falls to the floor or even near it.
I recently had a commercial shop exchange the brake fluid on my wife's car and I've always noticed that brake pedal feels a little softer but with more braking control after a flush. To me that's better.
Could it be that my dad was just so used to crappy braking with 10 year old fluid and now it feels weird to him?
I can't see anyway that a pneumatic bleeder tool would be able to introduce any air into the system as it just sucks out one way.