Downtube shifters are cool from a C&V perspective; my first road bike in the early 90's had them, but I'm not sure why anyone would prefer this setup over modern drivetrains. They are definitely NOT the equivalent of comparing auto/manual transmissions in cars. It's more like comparing power windows to manual cranks. They both do the same thing, one just requires slightly more effort.
It's also worth noting that bikes with DT shifters likely have far fewer gears than a modern 2x11 (or 12). So... you'll be doing less shifting in general which makes for a different riding experience. I used to vary my cadence a lot more than I do now.