Wolfman gear is great. Really high quality, and you can't go wrong with it. That said, I kind of think an tailbag is a bit of a waste of money. I mean, a tank bag is pretty specific. You really can't strap any old bag to your tank without fear of scratching it etc, but a bag that straps to your seat, well you can pretty much slap any bag on there with a $3 bungee net. I've been using a generic Waterproof bag for years this way. It's big, tough, totally waterproof, and was like $20. I think I intended it to be used for kayaking, but it's mostly used on the bike.
If your spending any coin on it, I think a top case is so much more convenient than a tailbag. I have a Givi Box and rack on the Versys, but it was on there when I bought it. If it wasn't, I would have just made a rack as mentioned, and used one of those JC Whitney Top Cases (garage pro is the brand I think). I did that on my other bike. Made the rack from Steel Stock I got at Home Depot, and a black cutting board stolen from my wife. Was a fun project actually. I think my "All in" cost was like $50. Works just as well as the Givi. When loaded for a long trip, I run a strap around either topcase, as extra insurance they don't open or fly off. I don't have full trust in either one's mechanism when fully loaded, especially with my CPAP machine, or my laptop in there.
That's my .02, but I'm pretty "frugal". I do love my Wolfman tankbag which I've had for close to a decade. Here's a pic of the whole setup, including wolfman tankbag.