The cassette mounted on the R&M Birdy Touring is a 9-32t. This range is enough for most uses without the need of a double crankset and weight much less than a CS-RK3.

On my Birdy, I replaced the Sunrace rear hub and cassette by a Tune hub+Ethirteen 9-34 cassette+Shimano RD-R8000GS with a little more range and less weight.