It's because she's no longer a precog that I think it's an adequate countermeasure. The first thing we found out about Feathers is that it defeats her precognition. I expect her clairvoyance to be a different matter entirely, especially given how it's the strongest clairvoyance in the setting.
Feathers can do things and create futures that Oriko didn't predict, yes, but that's also part of what made Oriko's precog a perfect way to detect that Feathers has done something, and what it is that they did.
Like, when Sayaka got yoinked over to Elsa Maria, Oriko's visions of the future immediately changed, and through her observing those new visions we knew what it was that changed very quickly, which enabled us to take swift action.
Oriko's clairvoyance, on the other hand, might not be "disrupted" by Feathers in the same way - and thus whatever Feathers might've done might be harder to find out.
It might still be adequate, but that's why we should talk it over with Mami, Homura, Oriko etc first, to see whether or not
they like the risk-benefit analysis here, and what they could bring to the table to try and make it safer.
(EDIT: Also, I do want to mention - I'm personally only really inclined to do more Barrier experimentation unless we're at least decently confident we can
prevent additional Feathers shenanigans from happening, because I fear that the consequences could be worse and less easily solved than just a Sayaka abduction. Maybe Feathers will take more extreme action next time, or perhaps every time Feathers goes active there's a risk of Feathers finding whoever it is that they're looking for and/or linking up with Homura or something, or perhaps Feathers will permanently become more active each time...
Part of the reason I'm insistent on talking the idea over with our friends is because I don't think we have enough data/sufficiently compelling theorycraft to be able to make that call yet. I wanna hear their input.)
Yes. Something rendered the invisitext unable to see us during the sleepover at Madoka's. That's a lot of where the thrust of my vote comes from.
Hm. So if I'm understanding you right, you think the reason Feathers couldn't see us at Madoka's was because of some kind of "rule" or restriction on it?
I hadn't even considered that - I'd mostly just gone "eh, maybe Feathers lost track of us or something? or maybe Feathers hasn't found us yet
in general, and something bad will happen when it does?", but I hadn't thought about it too deeply yet.
I'd be interested in hearing more of your thoughts on the matter, if you have them.