The larger sized ones can be quite good- like the OG Theorem notch coil. I've only seen SS "coils" for rebuilding, not really prebuilts other than the Cuboid/Cubis stuff that was a bit marginal. All work with SS TCR.
Yeah, that plus SS makes them great for TC. Unfortunately they're already old tech, never caught on, hard to find. Mesh is the new notch. Better, cheaper, easier.
Thanks @Vapin4Joy for your feedback.
I am asking becasue I came across a few of them on Fasttech (Notch coils search)
And there are a lot of different sizes for RTA's