I bought a Mags Bag Voyager model. It comes with a rain cover, plastic D-rings and nylon webbing straps with a loop sewn on one end. You loop the straps through your frame, then thread the open end of the strap through the D-rings. The bag is well made except for the plastic D-rings. Two of them broke when I cinched down the nylon straps. I replaced the plastic D-rings with stainless steel D-rings, but they were too slick and the nylon webbing would not stay cinched down. I bought Rok Straps this past summer with quick-release buckles and they allow me to quickly secure the Voyager bag (and anything on top of it) to my pillion seat and quickly remove it when I want to. The Voyager bag comes with nylon bungee cord on the top flap, which you can use to secure a tent, thermarest, etc.
For the money I think its a good bag, but it wouldn't work for me without the Rok straps. You should not look at a soft bag as an alternative to a trunk. I mounted a Givi Maxia 52 trunk on my FJR and use it all the time, both around town and on long trips. I use the Voyager bag when I am going on a long trip and want some extra baggage capacity that will keep the contents dry. I put my rain gear, extra clothing layers, gloves, food & anything I need quick access to in the trunk. Keep in mind that the trunk extends well past your rear axle and shouldn't be carrying much weight. The soft bag mounts on your pillion seat--over your rear axle. You can put much more weight in it and on top of it with much less adverse effect on the bike's handling. The soft bag will hold stuff that you just can't fit in your side cases. And yes, you can stow a computer in the soft bag. I carry a Mac PowerBook in mine wherever I go. The Voyager is wide enough that it comes out to where the side case lid meets the black plastic "bottom" of the side case--just right in my opinion. I can open the side case without dismounting the Voyager bag, but I have to hold up the "end" of the Voyager bag a couple of inches to put the key in the side case and pull up the flap--no big deal.
One other problem I had with the Voyager bag was that it slid down to the front and pushed against my lower back. As you know the FJR pillion seat slopes up to the rear. The Voyager bag has a level bottom and the stock D-rings are on the bottom, so the bag wants to scoot down toward the rider. If you pack it full, it can push against your lower back--pretty annoying after 200 miles. I stuffed a folded up rain tarp on top of the pillion seat and under the Voyager bag to level it up, but it still sagged when using the stock D-rings. Using the Rok straps on the Givi trunk mounting frame solved that problem. The Givi trunk mounting frame sticks out from under the side of the pillion about half-way back on the pillion seat. I attach the front Rok strap to the front end of the trunk mounting frame. I attach the back Rok strap to the trunk mounting frame right ahead of the front end of the trunk itself. One end of each Rok strap has a stretchable fabric. The other end is nylon strap that you can cinch down against the quick-release buckle. I set the loaded Voyager bag on top of the folded tarp (on top of the pillion seat); I clip and cinch the Rok strap and it snugs the Voyager bag back against the front of the Givi trunk. Voila! No back pressure; but I can lean back against the Voyager bag when I want to change my seating position.
Bottom line: Mags Bags are good products, but need some modifications in my experience to work well. Soft luggage is not an alternative to a trunk. They are both part of the solution if you are doing long distance riding. If you are just riding around town, mount a trunk. Last comment: if you think a 52-liter trunk is too damn big (as I did at first), put it on. Within a month, you will wonder how you ever got along without it and you will think it is too damn small to hold everything you want to put in it.
Good luck!
