Bruce:

I still have that one Schlumpf SD from you... I bought it specifically for the Birdy, even though at that stage I was unsure of what I would be getting.

One reason it isn't installed yet, is the Birdy's rear swivel arm has a slight depression where the chain goes past. I'm unsure at this stage whether the smaller chain ring required by the Schlumpf will cause regular chain rubbing.

Unrelated Schlumpf questions:
1. Do you get the gear shifting buttons unscrewing? I have a few times just caught one or the other button before it fell off mid-ride. I have made a tool for tightening but that hasn't helped. The locking set screws are as tight as I dare. I daren't use Loctite for fear of not getting the button off again when I need to. Any thoughts?
2. Do you get slippage of the bottom bracket when in overdrive? This has happened to me a few times now, not very bad though, but enough that I avoid hard cranking in overdrive.