I’m after a 42t cassette expander and came across these:

http://www.tredz.co.uk/.RSP-Cassette-Expansion-Sprocket_77603.htm?sku=248737&utm_source=Google&utm_medium=AdwordsProductAds&utm_campaign=Adwords&gclid=CjwKEAjwmZWvBRCCqrDK_8atgBUSJACnib3l1HnYopfFVMBiPPEW8eNrBBL5-xziiNZOy4ZNCYaGTBoCqMrw_wcB

Just wondered if anyone is using one and how they are getting on?

thanks