The Fleetside Slants are great. They hold shape well and yet can be stuffed to hold much more than one would guess. The bags fit the bike without relocating the turn signals, though fit is tight all around -- next to the turn signals, above the pipes, and behind the passenger foot rests. The bags are soft enough that the turn signals aren't a problem, the stock pipes stay cool enough that a half inch of clearance is enough, and I've gone on a week-long trip with a passenger without any complaints. The only problem I've had is that the bags reach down to just under the bottom of the shocks, and when they're empty and sagging against the shocks the up and down motion tends to push the shock against the bottom seam of the bags, which after a while (6 or 7k miles, in my case), rips the seam. I think this can be relatively easily remedied by an L-shaped insert that would keep the inner side of the bag perpendicular to the bottom. Saddlebag supports might also help, but I don't have them. I got the bags from MAW for about $140.
The Tour Master bag is very convenient, though I wish I had gotten the XL. It flexes to hold large objects such as my full-face helmet without trouble. I've had some trouble with the barrel bag, however. It's meant to attach to the main bag with a zipper, but some of the teeth on the half of the zipper that's on the main bag broke and others got knocked out of position, rendering the zipper useless. A conveniently located D-ring on the front of the main bag can be used for attaching the bag with straps -- luckily so, since the zipper broke on a longish road trip. I bought the bag from Sherm's for $100, but unfortunately getting a replacement bag wasn't guaranteed and was enough of a hassle that I haven't bothered, since I use the bag daily and couldn't be without it for as long as was necessary for the return. I'm not too displeased with it overall, but if I were buying again I'd probably get a T-bag or else a custom lockable container of some sort.
The only noteworthy thing about installing the Mustang Wide Regal is that it doesn't fit quite right when a rear rack is installed. The stock seat has a contoured bottom to accommodate the rear rack and its mounting bolts; the Mustang doesn't, so it sits just a touch too high to match the screw holes in the sissy bar. Instead of cutting into the bottom of the seat to create room for the bolts, I merely enlarged the holes in the sissy bar by about 3/16". I got the Mustang from Accessories International for ~$300.
I opted for the Wolos instead of a more expensive brand. I mounted the horns on an 8" aluminum strip that I attached to the left front of the frame at one of the engine mount points with the bolt that was already there. The compressor and relay I put under the left side cover next to the fuse box -- there still seems to be plenty of space there. I put an in-line fuse between the battery positive terminal and the relay, and dragged a horn switch ground from one of the spade connectors that were attached to the stock horns. I ran both that wire and the vacuum tubing from the compressor to the horns along the left underside of the tank to the front of the frame, and then up and down along the frame -- it's completely unnoticeable. Mounting took me a couple of hours but can probably be done easily in 45 minutes by someone focused on the task.
I love the horns. They're loud enough to get people's attention with no trouble even at highway speeds, and I love the startled and slightly frightened looks they cause. They make me feel quite a bit safer since I know I can make my presence known in cases where before I couldn't. So far this has been my favorite addition to the bike.
Parts used: Wolo Airsplitter, ~$45 from AutoBarn.com (in the box were two horns with a mounting screw each, a compressor with a mounting screw, a relay, about two feet of transparent tubing, a Y-splitter for the tubing); aluminum strip from Home Depot (8" x 1" x 1/8"); some spade disconnects and a heavier connector for the battery positive connection, also from Home Depot; 5' of 14-gauge insulated wire; 5' of 1/4" vacuum tubing from Pep Boys; an in-line fuse holder and fuse from Pep Boys. Total cost was ~$60.
[ See my KLR 650 page. ]