Here is take two on my dust boot. I made it easier to print, and opened it up more for better suction. Finally I redesigned the brush holder to be both more flexible and hopefully prevent the brushes from being sucked into the vacuum. The idea is to support the bristles (or whatever you use) as much as possible without restricting the ability of the brush to bend.

I'm experimenting with low cost alternatives to bristles. I can't find brush material for less than $10, that is about 1/3 the cost of buying a dust boot on amazon, so a bit pricy. Anyway right now I'm using a section of a ShopVac foam filter sleeve I found at Walmart for $4. I'm using 1/4 of the filter, so it could be used to make 4 brushes. I have not tested it out but I think it will work well, it is solid, and yet can easily be compressed and should prevent chips from flying out.
If that is a dud, then I designed this to take 70mm bristles. I will try that out next. Fingers crossed for a good test tomorrow.

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Well it works a treat! I don’t see any down side to using a piece of shopvac filter for a dust boot brush. You could probably use most any porous foam material like a scotch brute pad or chair foam.
I don’t see any dust outside of the cutting area and 90% of the dust in the hole was sucked up.