I have a Rubberset Aluminum #3 and have been mulling over they type of knot to use. I'm not into boar, but that Omega looks great in that handle. Very reminiscent of the knot the handle originally cam with. Interesting!
I don't want to reignite the whole badger vs boar debate, but to me, this one cried out for a traditional boar knot. And even the little black collar that Omega uses for its knots fits the look of the metal handle well. Anyway, I get to try it out tomorrow, so we'll see if the whole package works as good as it looks.
Used it last night, and it's definitely a keeper -- the Omega knot is just the right size for the handle, and it's like the brush came with that knot originally. If you're going to put one together yourself, get the small Omega knot from Tony -- the 22 mm one. The bigger ones he sells are just gigantic, and with the plastic collar, they just don't fit into any reasonable sized handles (except for a vintage #5). The small Omega he sells fits perfect in this #3 handle with just a little bit of shaving and sanding.