It is generally found that slip rings are not required in most installations. On average the mill turns evenly both ways, or at least does not require unwinding very often.
One of my units, an old commercial job had slip rings origionally but I did not refurbish them with the mill. It also had bearings on the piviot, I had to unwind the chord weekly.
I currently have a different unit on this tower that has pipe over pipe with a brass washer as thrust. This has been up for nine months and I have not had to unwind it, so this tells me for my situation some resistance to yawing is desirable.
Some believe slip rings are another source of resitance best done without, others are happy using them. Not everybody has the expertise or equipment to manufacture sliprings so take the path of least resistance.
Allan down under