Always be polite. It does not help to be impolite, critical, or derogatory. It is a good idea to thank the referee for help given, and if that help is substantial, it can be acknowledged in the text. After all, the referee gets no credit for his work other than your thanks. You are welcome to inquire about progress after that.
Editors normally ask potential referees whether they can review the manuscripts.
Sometimes the first person declines because of travel or other conflicts. The reviewing time can be lengthened when a second referee must be sought. That is much cheaper. Tables prepared electronically cost less than ones requiring typesetting.