When I bought the car the new style pump was already there; but I have on the job experience with the older style ones. I like the new style Primer Pump better.
If you are using VO it may be that the VO is thicker and harder for the new stye Primer Pump to move and as the other member said the new style Primer Pump may move smaller amounts of fuel when you pump.
Also last year there was a member who got a new, new style Primer Pump and it was no good. He went back and got another and that one was also no good. He took it back and got his money back and went to another parts supplier and bought another one that turned out to be a good one.
He figured with 2 bad pumps fromt he same place there must have been a defective "Lot" of pumps. Going to another seller reduced the chance of getting another from that defective Lot.

__________________
84 300D, 82 Volvo 244Gl Diesel