Pythons are essentially gavel tubes with extended hoses that connect to a adapter that hooks up to your sink (think waterbed emptier/filler). Essentially, the flowing water from your tap creates enough suction to start the flow of water from your tank, one switch of a knob (so to speak) and your python turns into a tank filler, thus eliminating the need for buckets. You can add dechlorinator during the filling process if need be.
I would recommend pythons if you have larger tanks, or many tanks (or a combination of the two). If you only have a few smaller tanks (ie. 20 gallons and below) and you don't mind a few bucket trips, then a python isn't really needed.
I use a python on my 66, 70, 15 and 20bowfront tanks, works great for me.
HTH
-Richer