what would you benefit from fitting a 1 piece over a 2 piece?

obviousley a slight torque loss but less flex ad centrifugal force surely?

converted a mk2 escort to pinto and 1 piece prop and vibe was that bad you couldnt touch the g/knob over 50mph!
everything was off and checked 3/4 times and balanced twice, new prop but never got to the bottom of it.

2 piece prop fitted and car was so much smoother, seemed to accelerate faster over 70mph too, may have all been in the mind but noticable drivability gains.