I have a Parts Unknown sight on my Sharps. They seem to be sturdy enough. I'm rather impaired reading micrometer readings, and need more practice with the sight. John King mentioned one he felt was easier to read last weekend, but I don't remember the maker. He also mentioned it was cheaper. Al in all, I'm happy with mine, and I know quite a few people use them.
Mine seems to have some lash in the windage and the adjustment is kind of stiff. I have been told I can put an O ring in and take out the lash but have not tried it. I have also heard, but do not know from personal expierence, the maker/importer can be difficult to contact and slow to respond. I think the parts unknown sights are usually considered less expensive than the other sights.
I'm no machinst, and know nothing about set up time, but I personally feel that all of them are a rip off. That ain't a bunch of metal you are getting for that many bucks. Maybe I should put the Chinese to work making some for $30 bucks a copy...