That's interesting. can you please link to your OSPW? On the er9, if you run 11-34 (native) or 11-36 (with a small cage extender), in small small, there's a lot of chain slack. Mind you, the app has "gear protection" that prevents that, plus you shouldn't cross chain, but if the OSPW acts as some de facto clutch, it becomes a lot less useless as an upgrade, at which point i'm curious to try. And I agree w you, i'm not paying 500$ for that farce.
It then becomes a question of whether there's an OSPW option for the er9/x.

Avoid these cages at all costs. Broke two of these, last one on a cobble section in a race. Pure garbage! Consider yourself warned

I've broken chains but never a quick link of any brand or type. I reuse them without any second thought until I retire the chain.

If I break a quicklink tomorrow I'll be singing a different tune!

In the last few days, the er9 RD of a friend died for no reason. Got stuck in the hardest cog and nothing will make it shift, including reset, unplugging, replugging and everything i could think of. The FD works fine.
Then today, went for a ride with my gravel bike, and my own RD died exactly the same way! I went down a descent with bad asphalt and vibrations, at the end of the descent, dead RD.
I'm trying to get a response from l-twoo via the intermediary that sold me the groups, I'll keep you posted.
But as of right now, I'm extremely unhappy and would not recommend er9/erx because a bike has to work, if you can't trust your derailleur to shift, then buy something else.
I'll post updates.
TWO DEAD er9 RDs in one week under normal use.