I haven't used them myself as they were purchased as a gift. Even if there are flaws, the concept and price make them a unique gift that you can use to supplement a bottle of wine.
I bought this for a friend's housewarming, and it was a great gift! She's a teacher, so the blackboard theme worked out well and the ability to chalk the coasters is a lot of fun.
Great host/hostess gift. Fun and practical. Helps guests keep track of their drinks... fewer extra glasses to clean.
We've been collecting bottle caps from breweries all over the US in a jar and now we can actually do something with them. My husband loves it!