rolled ball screws

Hi,

I am in the process of building a small CNC mill and would like to use
rolled, preloaded ball screws and nuts. The cost of these rolled
components is not much higher than Acme screws and nuts. The ball
screws are preloaded by placing larger balls than usual in the nuts to
take up any slack.

Does anyone here have any experience with these types of components?
How well do they maintain zero-backlash over time? How long does it
take to break them in? Reliability?

Thanks

Steve