When you're moving to a bigger incubator, usually people want to save as much money as they can, but the incubator still be in good working condition. Look at both of the incubators... Which one has a better reputation? Which one seems to work better for more people? Which one seems to be more advanced, meaning will it improve your success for the hatch rate? Does the used one seem to be in good condition?
If you were to get the Rite Farm incubator, you would essentially be paying almost $2.50 each egg you can place inside, and around $3 each egg for the Kuhl incubator. The Rite Farm incubator is less expensive that the Kuhl incubator. Then again, you also have a 72-egg difference, one is used and the other isn't. Does it matter to you for how many eggs you can place in the incubator?
I think you should ask the person selling the Kuhl incubator if you can go check it out to see the condition it's in. If you believe it's not in that well of condition, I suggest going with the Rite Farm incubator. I know that probably sounds confusing, but I hope that helps!