Hi Al
I have a Warco mill which I used reasonably successfully for about 18 months. Then I noted the advice from many different posters on here in many different threads who were largely of the same opinion, that a DRO transforms mill operation. I now have a magnetic track DRO from Machine DRO, whose advert appears on the right of this page, on the X and Y axes of my mill. The downside is the cost of this system but having considered some of the cheaper options with small displays and scales which were not fully proof against ingress of moisture (such as cutting fluid) I am more than pleased with what I have.
It has many different functions (most of which I haven't used yet), a large display and easily useable programming buttons. The first and most obvious benefit is that I no longer need to consider the problem of leadscrew backlash when moving the table. I no longer mark out my work as comprehensively as before, using the DRO to position the job and using the marking as a confidence check only. I would say definitely go for it and get the best you can afford, it can always be transferred if you upgrade the mill later.
I cannot comment on 2 or 3 channel as my mill has an electronic depth display built in so I never even considered the Z axis but I am sure others will be along shortly with more advice based on more experience than mine.
Jim