You can only use it within 60 days of checking-in. So it basically grants you access to a free last call week somewhere in RCI inventory. And even all of the options it gives you are not "free", most of them are considered to be "upgrade" inventory and you have to pay an additional fee to book them with the certificate. Some of the upgrade fees are like $149 for the week which is reasonable, some of them are several thousand dollars, and completely not worth it.
The certificate would only be useful for a "free" week stay somewhere if you don't mind traveling in the off season and you are very flexible and not too picky about your accommodations. They may tell you its a free week stay at any Wyndham, but I have seen very little Wyndham inventory available at all- mostly small independent type resorts with an occasional Wyndham week appearing.