These are re-releases of the Allen Keller "Great Model Railroads" videos that were originally released as VHS tapes over a span of 20+ years. All of them will be indoor O, HO, and N scale layouts.
Our club was given volumes 1 through 53 a few years ago, and I don't recall one single G scale program among them.
As the enclosed literature indicates and has been discussed on the Trains and Model Railroader magazine forums over and over, you can either keep the disk as a gift or send it back and request that they send no more. Otherwise, you'll probably start getting one every month and will be billed $29.98 or so for each one.
United States Postal Service regulations state that you are under no obligation to pay for unsolicited material so even if they do start sending you a different disk each month, they can't make you pay for them unless you specifically subscribe to the series by returning the enclosed card and indicating that you do want to receive future issues.
If you don't like it, simply put it in the enclosed postage-paid envelope together with the card and send it back.