I have a Cosina 100-300 from film days, which worked quite well on my first DSLR, a K110D.
After losing interest for a while I then bought the K70, and went through the usual Sigma 70-300 enigma variations, as they are so cheap second hand.
Then to the DA-L 55-300
Then the DA WR version of the above
And then finally to the PLM which I love.
It isn't that any of the above are BAD lenses, I have (in my opinion) good shots from all. But the Sigma's were hit & miss for quality, my DA-L was/is very noisy, and I found the DA WR hunts a lot for focus on the K70.
The PLM is simply miles ahead because of quick, silent focus which when shooting bird life is a godsend. Image quality is excellent and colours rich but natural.
I think the guys & gals who designed and developed it need a bonus