Yup, I've used the Saint RD on my Touring Birdy Asian model. It's just a regular Shimano RD that can be mounted to the Birdy without any problem. What you need to consider is its capacity. It only accommodates 28T differences. The Saint and Zee RD were built for free-ride/downhill bikes. These bikes don't need frequent shifting like other types of bikes. The shifting on lower sprockets can be slower due to its slightly lower tension with short cage length. It is just how the design is.

I did a test with a hacked XT M786 and till today I'm using this test setup. Both M786 and Zee/Saint cages share the same connection mechanism. I put the cage from Saint RD to the M786 RD. I still got the slow shifting problem at 11/13T. Real-life usage isn't that much of a problem. I just have to wait for like 1 to 2s and it will still shift down to 11T.

I won't suggest you to use this with a double chainring setup due to its limited capacity at 28T. The RD was built to use a max of 11-36T cassette.

Another problem with using a MTB RD is that, folded width becomes wider due to the fact that the corner edge of the front fork (where the skewer is located) will be blocked by any Shimano RD with Shadow+ design. The front fork can't really be tugged into under the rear side of the RD like other non-shadow RDs.

(This Asian version Touring Birdy 3 came with a SRAM DD3 IGH. The cylindrical bolt is a custom-made part by Pacific Cycles to replace the original DD3 click-box. The newer version of the bike now comes with Sturmey Archer CS-RK3 IGH. Serving the same purpose of a hybrid 3x8s to 3x10s setup.)


(Left) Saint, (Mid) Hacked M786, (Right) Folding problem.