For a long time, I was able to get away with cutting all of my Dado joints with a straight plunge router bit. Although not ideal, I was never able to justify the expense of purchasing this cutter.
I would simply mark the depth and width of the cut, set up the depth of the cutter accordingly and then set up a fence to get a straight line. To achieve the right width of the cut, I would then move my fence over to make the second pass.
Depending on the depth of the cut, each set up may need a couple of passes because of the (blank) of the router bit.
To be honest, it is quite hard getting perfect and identical results using a router when you need to replicate the same dado cut on numerous pieces.
I remember one occasion when I needed to make a project which called for a lot of Dado and rabbit joints. When I put together a quote for the client, I realized how much time I was billing for cutting these joints. It was unreasonable, and even a bit embarrassing to realize how long this project was going to take me. I needed to find a faster way.
I was able to solve this problem by using a stacked Dado cutter. I was working on a budget and tried to get away with the tools I had, but this time I was able to justify this expense. In the end I was able to cut perfect joints, replicate them a few dozen times, and do it in a fraction of the time.
I have to say that setting up the cutter for the first time was no picnic. It took more than a few test runs to make a perfect joint, but once I had it set up, it was a pleasure to work with.
Read about Stacked Dado Sets vs. Wobble Blades.