As far as I know there is only one model, but I'd be careful of getting something like that off eBay. How would you be able to confirm that it worked before you bought it?
There is only one tailgater but there are several similar products on the market. You will need to have a ViP211k to be able to use the tailgater. If you have specific questions, please PM me and send a link and I will look into it for you. Thank you!