The CKE 3, 4, 5 are kind of like Pentium 1, 2, 3.

They will all run the same software, but have different levels of processor and chip set capabilities. For most small users, CKE3 will work just as well as CKE5. The larger users with more stations and complex programming will need a CKE4 or CKE5 to handle the processing better. You will have to get into the programming to see what software version they are running.

The FM units were Merlin II and had firmware plug ins for the different software levels.