Hello Caroline, What an interesting machine!
I've looked on the Needlebar website, and they don't give much on Adler, and there are no photos of this model. It looks as though it is longer than a Singer 128, and it has a couple of nifty German features. Singer never put reverse on long bobbin machines, but the Germans had that one worked out early on. My 1913 Serata treadle has reverse. Also the plate on the bobbin winder will automatically disengage the winder from the balance wheel when the bobbin is full, something Singer machines didn't do.
Once the machine is all cleaned up and back in its cabinet you will have hours of fun with it.