Permeate pumps ONLY work with a pressure tank period. Without the backpressure they do not function at all.
4:1 is not a claim, its what they are supposed to be set at with or without backpressure with a properly designed system. Many vendors use fixed type restrictors, most better vendors use capillary tubes which you take the time to trimn for an exact waste ratio. I wouldn'y own a fixed restrictor, RO is not really a plug and play or one size fits all. A few minutes fine tuning can extend the life of a membrane by years and reduce unnecessary waste significantly.

All of your comments need further research. I can provide more documentation if it would help.