There should be more disclosure, but at least they say "$x OFF" rather than "we'll give you $x"
So you know you have to purchase something.
And $5 off $15 if not bad if the $15 is reasonable to start with.
...but there are so many that say things like that then you see it's something like $5 off $50 order, but only on Wed, and not during peak hours, and ...

So if they don't want to disclose terms up front, I figure they are probably not worth the click...at least let me know where to find the terms before I commit anything, even a "Like"