i'm looking for a spider-based PM as well, but kind of getting confused between PES 505 vs 515 as it seems like the latter is newer but is only offered as a PM+crank set?
If i'm correct, does that mean i need to get the P505 if I only want the spider PM?
the P515 is the newest version, accuracy is about the same but it's a little bit lighter by ~10g. the P515 only fits Magene branded cranks arms. the P505 might still be available as a spider only in some places but it only fits a limited number of cranks. if i recall the P505 spider only fit SRAM 3-bot, SRAM 8-bolt and Rotor crank arms.
the best bang for the buck that has fitment for the most different styles of crank arms is Xcadey. out of the box, the power numbers from Xcadey tend to be off by about 5% (low) but that can be scaled in the Xcadey app and it's fine after that. I have Quarq, 4iiii, Xcadey and Assioma power meters and they all work about as well as each other - 4iiii probably being my least choice since it's just a left arm PM but the result is still minimally different from the others.
