New cassette and chain time not ready to jump to 11speed yet circa £170ish Need cassette and 42t extender.

One up are an eye watering $80=£55ish

Uberbike are slightly less tear inducing at £30.

Any reason not to get one?

Yup, they work.
You don’t get a 16t with it – so I just didn’t bother with one. Had OneUp and 16t before which also worked fine. Both with an XT mech with Radr cage.

Superstar make a cheap one too. Mine has been fine. Also worth looking at cassettes from sunrace and praxis. All in one, ready made. Iirc the sunrace is a decent price compared to buying the bits if you need a new cassette anyway

this may be work a look:

http://www.workscomponents.co.uk/chainrings–cogs-19-c.asp

Praxis/Sunrace 10s wide range cassettes probably worth considering if you need both cassette and expander.

SS out of stock of 42t and works don’t list a 42t.

I’ll try the uber as I have a credit for merlin, XT cassette reasonably priced.

Uber’s’ll most likely be a carbon copy of someone else’s so it’ll work fine.

If you want to change to a 16T then shimano’s is the best option anyway, that was always a pain in the bum but Bird sell them now. I’ve done it both ways but it’s worth changing imo.

SBS10 was a discount code sent to me late last week for 10% off at uberbike

Sunrace MS3 is £42.50 at Triton – working well for me…

MS3 cassette

Here is my maths on working on which route I want to go down for a 10s 40t setup.

Ready made cassette from Sunrace:
MX3 (40t) – £53

Expander ring and new cassette:
SLX – 40t (Uber) – 16t OneUp – £62
Xt – 40t (Uber) – 16t OneUp – £74.50
Xt – 40t (works) – 16t OneUp – £66.50

(Note: the SLX you would need to manually take apart by cutting a pin holding the cassette together)

Will also be cheaper if you can find a Shimano 16t sprocket off ebay or some oneline shop for £4-8. The OneUp 16t is £11.

addy6402, what mech are you using with that Sunrace cassette? I’ve got the Shimano SLX but heard you may get shifting issues with the 42T and a Shimano mech?