We purchased one certificate. It was worth $25. I don't remember what we paid for it but I think we ended up getting it for around $12 or $13. If I remember correctly, we figured one adult pretty much ate free. With using the $25 gift certificate, my husband thinks we paid about $5 out of pocket plus tip. We had 2 adults and one child. I don't know if they still have them on EBAY or not, but if they do, make sure you read all the rules. I don't know how many you can use at once. We purchased quite a few of them for different places and some had a minimum of 2 and some of 4. We had to save the ones for 4 for the days that our 19 year old was with us. I think the restaurants.com website sells the certificates for half price.
As far as days to go, we called the Grosvenor directly and asked for the restaurant. They filled us in on the days they offered it and the price. I thought it was T, Th, and Sat., but I am probably wrong.
I hope this helps. Debby