I've used the certificates many times and have, mostly, been happy. In California the certs have never expired so I have a few that are several years old (bought when 90% off). I tried to use one at a restaurant we had used one at about 2 months before and they said they are no longer accepting. I found this out before we ordered, so we left.
Got a few before a trip last year to San Francisco. 80% off. One place we went to was not good, kind of dirty and we didn't find anything on the menu we liked. At another one the service/decor/menu didn't warrant 18% tip. It was pretty much a seaside funky dive. Oh well, live and learn
Have used them many times for HoB in DTD in Anaheim. If I figure it just right it works out to a 50% discount, which is pretty good.
If you are going to get some for vacation, the fine print states that you can only use one coupon a month. That's based on a calendar month, not 30 days. So if you plan on going to a location more than once in the same month, use a different email, etc. to get the second one.
We have never had a problem using them at HoB. The are one of the few restaurants that count beverages as part of your required total. Makes it much easier to reach the min. $35 with $25 cert.
I bought one for HoB in WDW last year and with free
DDP didn't use it. I'm giving it to my DSis to use on her trip this month to WDW.

If she doesn't use it, we can use it ourselves in October.
I have had a few of my restaurants close before using the certs but they do credit you back for the cert.
Someone asked if major chains participate (Applebees, Olive Garden, etc.) Not that I found. They don't need to to get people in the door.
Always wait for a sale. I never buy until they are 80% off. Makes the $25 ones only $2.

So, for example, when I can get my check to total right around $35 (I even added a topping to a pizza at HoB for .70 to get this to work) this is my breakdown, at HoB, in Anaheim.
Meal, before tax, inc. beverages $35.00
Tax on $35. (8.75%)---------------3.06
Tip on $35 (18%)------------------6.30
Total----------------------------$44.36
Less $25 cerfiticate--------------$19.36
Paid for certificate----------------$2.00
Total paid for meal---------------$21.36
Total saved----------------------$23.00 saved over $51%.
Now this is the best case scenario. The more your total is before discount, the small your percentage. But I think it's worth it.
