It's real, just make sure you understand the conditions of each restaurant. Some limit days you can use them, most say only one per table, some are one per 30 days, etc.

For example, from one local place (leaving many conditions out):

Must present gift certificate prior to service. Valid with party of 4 or more.


TERMS AND CONDITIONS
• Limit one (1) redemption per party, per month, per restaurant.
• Limit one (1) dining certificate per redemption. Only one dining certificate can be used per party, even if the party is seated at separate tables and/or receives more than one check.
• Use of dining certificates for alcoholic beverages is at the sole discretion of the merchant.
• Dining certificates cannot be used for taxes, tips or prior balances.
• No cash back upon redemption or at any other time.
• Valid Tue-Thu, Sat for lunch with a minimum purchase of $15.

etc. I'm not a huge fan of the must present prior to service places, that makes you wonder.......Some are cash only, etc.

But if all of that fits what you are looking for, yes they are a great way to save $20 on the check.