Singer was a dial producer for Rolex. There were a few others as well such as Beyeler and Lemrich. These dials were found on Rolex watches until more recently when Rolex purchased one of the manufactures and brought everything in-house. Service dials are post-production, and were sometimes made by the original supplier (if prior to establishing the in-house capability), and sometimes by Rolex itself. These service dials were put on during a servicing, and thus are considered by collectors to not have the same value as an original-to-piece dial. They are still genuine, but would never be found on the watch at birth. Many of the "repainted" dials you see are not actually repainted blanks - more likely they have fake Singer stamps.
MQ stuff is very good, but also very, very expensive. Marginal cost of the "correctness" is high compared to some cheaper options like Ruby's or Helenarou, but at the end of the day they are your dollars and the utility measure if your own.