I used a 5ft Rhino rear finish mower on my CK20. No issues at all. I also used a 4ft bush hog which was about the right size too. If I had to do it over again though I'd probably get a 5ft light/medium duty flail mower instead of a RFM. Cuts as well and is more manuverable and easier to store. Costs about the same. (eg Caroni TL1500 from AgriSupply)