Arcs, angled lines and inclines are achieved by giving the operator a series of moves to make, inevitably they are a bit lumpy and not intended to give you a finished cut - you'd have to make thousands of moves (like CNC) to achieve a finished surface, it gets you close enough to file to shape off the machine without a huge amount of work.

I don't think you get more from the PC based display, it doesn't mention bolt circles etc. it may do less -

http://www.machine-dro.co.uk/m-dro-p...interface.html

I'm not keen on fitting 2-axis readouts to 3-axis machines but if you can manage and it keeps the cost down...

These are the type which I'm using - http://www.machine-dro.co.uk/sds6-3v...s-display.html

I had a failed PSU in the display on the mill and called Machine DRO, they didn't have one in stock but could order me a PSU for it, I had nothing to lose so I stripped the PSU and found a 50p electrolytic had let the juice out, maplins had one in stock ;-)