hi, just wanted to check if this is for a MTB with 26" wheels?
At least to me, a 30T chain ring at the front is for a 26" bike too small, because you will end up in flat terrain to run the chain almost all time on the right cogs of the cassette.
I do use a few old 26" bikes with 1xX, often a 9 or 10 speed 11-36 cassette at the back, because you can use old derailleurs with 36T max. for everything bigger you need a modern rear mech, or tricks like goat link / wolf link, something I wouldn't recommend.
BTW: if you want to use 10speed with an a bit older Shimano rear mech, those didn't have Dyna-Sys and use a different gear ratio as newer 10speed MTB trigger and rear mech.
Older Shimano MTB rear deraileur (originally designed for 7-9 speed) do work with 10speed too, but need a 10speed road racing shifter (e.g. road racing flat bar trigger)
I do use them depending on usage with 36-42T chain ring in the front, mostly on flat or mixed terrain, but this is not adequate for steep and longer uphills. Just checked smaller chain ring in the front earlier, too me not allowing to drive with higher speed in flat or descending ground.