I am looking at an extended range cassette, there are a choice of 2 that look appealing is there any advantage compared to an extender cog.

http://www.westbrookcycles.co.uk/praxis-works-11-40t-wide-range-10-speed-cassette-p282704?gclid=CjwKEAiAtf6zBRDS0oCLrL37gFUSJACr2JYb_oy69R-gRgdomPsAQHN2HYQhVXiNDgzENI3ZKn3u6RoCvcHw_wcB

http://www.charliethebikemonger.com/sunrace-mx3-cassette-11-42t-10733-p.asp?gclid=CjwKEAiAtf6zBRDS0oCLrL37gFUSJACr2JYbbL4jPuBxcFUVv0O7gIlzwYTQtyymrFlc6brPZMxJgRoCUKHw_wcB

also is a 42 worth the miether?

I like the idea and I suppose they’re actually quite good value now they’ve dropped a bit in price. The Sunrace one looks especially good value.

I’m running the Praxis Works 11-40T cassette and it works very well. Have used plenty of expander cogs but the advantage of these is they do away with either the gap where you need to remove a cog or the not quite right 16T filler. Considering trying the 11-42 SunRace soon but you will need either a RAD case or new XT mech to cope with the 42T cog.

I have a Sunrace 11-40. Shifts very well.

I am looking for a 11/40 10sp but unable to find them in stock ( steel ring )
Any one used a 40t with a std shadow long cage rear mech ?

The Sunrace ones are on eBay

sunrace do two – mx3 and ms3 (ms3 is heavier and, of course, cheaper)