CVS Greene bag tag

I've been reading about this for a few weeks now, but didn't want to post it until I saw it myself at CVS. There are these Greene bag tags you can purchase for $.99 at the checkout.. You attach them to a canvas bag, it can be one you already have from home, and every time you make a purchase, have the cashier scan the tag. Every 4th visit, you will earn an ECB. Of course, you have to remember to bring and use your canvas bag each time you shop, which I have been having problems with lately. There is a rule though that you can only scan the tag once per day. So if you do multiply transactions during the same visit, you can only scan it once.