Who has experience with this?
From my own experience of owning 13 single coil/51 P-basses and trying 20 different pickups.
I liked the Duncan SCPB-1 though it had quite low output, I did not like the SCPB-2. The Roswell was fine, it and Duncan SCPB-3 share the same alnico pole pieces so have a similar attack; the Duncan high wire count loses Mids. The Wilkinson single coil found in PB-50s until 2018 is a very good pickup, look for one used. For a 'vintage' tone look to eBay, various Chinese sellers offer a low wire count (6.7k ohm) alnico 5 priced just €12. Years back I posted clips of 7 different 51 single coils on TalkBass, I use solderless looms so it was easy to swap pickup between recording the clips, then asked the "experts" there which one was recorded with the Chinese pickup. 80% answered wrongly
Hum-cancelling, be it stacked or split, cost you the aggressive edge of a true single coil. Think of it as a polite solution though as 'hum' is rarely heard over drums/guitars/keys is there really a problem in need of solving ? Sadly my 29.9k ohm custom was not the "Mudbucker" I hoped for
The Herrick Quad coil interested me though I found little benefit after installing it, an opinion shared by a fellow player who borrowed it. Another PB-50 owner told me the £105 he spent on the Fralin was a waste of money, he preferred the original Wilkinson. The offering from Lollar was another I considered, dropped the idea after watching the same one change hands 3 times in as many months through Basschat classifieds.
Things which will bring the greatest change to your sound are playing position and the strings you choose.