The single lens with a filter that has an aperture hole(s) in it is a very basic way of getting the light close to where you need it. It is a method generally used only in the lowest end of microscopes and is only "fairly" effective.
The Abbe condenser with iris allows the user to put that light exactly where they need it and at the correct size they need it. This gives you complete control over the light including where to put it, the size of the light cone as well as the depth of the focused light. This is used in mid to upper level microscopes.
Whether the Abbe condenser is worth the cost depends on your level of microscopy and your intended uses. The more features you desire or need, the higher the cost of the microscope. The ability to focus the light exactly how and where you need it comes at a cost. That being said, most of us around my age started in microscopy by using microscopes that only utilized a bottom mirror and we had little control over that light. I wouldn't go back to those microscopes voluntarily but it was good enough for a very, very long time.