It's my understanding that the legs on the leg-notch models extend themselves under spring pressure when you press the release button and they have locks every 1/2 inch up to full extension.
The non-leg-notch models require pulling the leg extension out by hand until it locks at full extension or you can use a thumb wheel/screw to hold it at less than full extension. If you press the release button, the leg will retract under spring pressure. I've owned a non-swivel model like this one in the past.
FWIW, I'm planning to get a bipod just like your 1) selection.