The open shop jobs I have had were good and bad but usually slower. This was largely because they were undermanned and with less skilled workers. This sometimes caused quality issues that forced us to redo portions of the work. It was cheaper but you get what you pay for. My experiences are from doing construction work in the Boston Market over the last 27 years. I am sure things differ greatly from market to market. I can only comment on what I have experienced doing 100's of projects with both union and non-union companies. There is one thing that holds true for Union companies. The owners are paying a premium for the labor so they are very organized and push he schedule very hard so they do not loose money. That is why I always chuckle when people throw out the "it's a union job" I think it comes from places where Unions have bearing on production like the NYC waterfront and the teamsters. That is a different dynamic from construction. Construction has contracts with liquidated damages when schedules get missed. These get shared with the subcontractors so working slow is usually not the concern. It's the quality that takes the hit so skilled workers are key.