They're OK, but nowhere near as good as hydro, especially when you have the flat bar options of all MTB brakes before settling on shimano. Those new XC hope brakes would suit this kind of build perfectly.
there's nothing wrong with them, but hydro ones are far far far far far better... plus that's (above) a flat bar bike, even entry level deore brakes will out perform the best cables in every condition...
There is also nothing wrong with Cable discs. Once set up correctly they are great.