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I've been using the 10s MTB version since 2015, it's a bit shonky, the index indent and the actual shift points don't line up to make a great shift if that makes sense but it's not so bad that I've taken it off. It's not work or got any worse in all that time and it's had a lot of use. I think the Sturmey bar-end @Alb had on his bike was the better option though - not sure if that was 9 or 10s and they prob don't make a 12.
Microshift barend shifter and TRP Hylex brakes is probably going the best the cheapest and easiest way of converting it...
https://www.microshift.com/en/product/bs-sr-m12/