I'm using an Aerobic Rider that I've had for a number of years and it works out the quads and the biceps as well as the cardio aspect of it. Presently there is a distinct mismatch and my legs get rubbery before my carbio starts peaking. But that is something that will correct itself over time. In the mean time, this is the approach I am taking:

Try to stay on profile as best I can until me legs and arms start giving out - the get off, rest 30 seconds to a minute and get back on and work for another minute to two minutes trying to build intensity if possible. Repeat this pattern as long as I can for the duration of the 20 minutes.

Today I did so-so. I had to get off after about 7 minutes and then was able to work the pattern for only a total of 17 minutes. My muscles probably reached a 9 but my cardio probably only reached a 7.

Again, this will work itself out over the course of a few weeks so I'm going to just keep going like this.