Making the chain hop from one sprocket to another looks like a crude way of altering the transmission ratio, but derailleur gearing can nevertheless work very reliably and most efficiently.
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For the greatest possible range of gears, so you can not only pedal down but also up the steepest hills, with the least possible wastage of effort (provided you keep the chain clean) and the greatest choice of ratios, derailleur gearing is the way to go.
The rule is: don't mix one make of shifter with another make of mech. But sometimes you need to bend the rules, especially when you want really low gears on a drop-handlebar touring bike.