I agree that the angle bracket attachment is too small and shaky. I've gotten a feel for it - but I need to concentrate on every face-plunge I do to make sure it's sitting right. I like this as a simple, fast, easy-to-make solution!
OTOH, I don't know if I'm too crazy about using the tool upside down and having to use a different jig for each offset / wood thickness. I have a whole bunch of left over 8020 parts from when I was making my MFT table (still working out a few kinks with that, but it's 95% done, will post pics soon). SO I used one of the really beefy angle brackets (2.75" x 2.75" x 1/4") to make the angle bracket shown below. I put the 1/4" MDF on the bottom to give it a little larger base than just the Alu and to give me a place to mount a little handle - it works WAY better than the standard angle bracket. I also took the advice of the folks here and put counter-sinks on the holes on the backside of the Alu for the rubber lock-rings for the festool thumb-screws. Only problem is that the screws are so long it's a little tedious to take on and off, think I may order a bag of M5 thumb-screws next time I do a McMaster order.
Thanks for stirring my brain in the direct of improving on the plastic angle bracket, I like this much better and wouldn't have thought to do it!
For anyone who's going to do this, the holes in the base are centered 50mm apart and 52mm back from the face of the tool.
Sorry the pics are a little messy - my phone and poorly lit shop.
Cheers guys,
Chris