Great Idea Mike.
Metal Mule panniers are British built and come in three sizes.
31L Skinny Mule - L470 x H385 x W206 mm
38L Classic Mule - L470 x H385 x W246 mm
45L Fat Mule - L470 x H385 x W286 mm
Top boxes come in two sizes
22ltr Stubby Mule
Height 225mm
Depth 315mm
Width 90mm
32ltr Classic Mule
Height 325mm
Depth 315mm
Width 390mm
The panniers and topboxes are available in a choice of finishes and you can add rubber feet, tie down loops and side handles as options or you can add your own choice as required.
Constuction is 2mm aluminium and are water and dustproof rated IP65. The riveted design is intended for easy repair in the event of damage happening in areas where finding someone to weld aluminim may be difficult. It is an unusual feature but one which has been incorporated in the R1200GS adventure panniers.
A single lock on the top of the pannier and topbox secures the both the lid of the pannier and the pannier to the frame. The frames are available for various bikes by a number of manufacturers. Frames could be easily made for many bikes which are not listed.
The panniers do not have an exhaust cut out but rely on either using a narrow pannier on the exhaust side or using the Metal Mule exhaust system (end can by Scorpion) which allows for equally sized panniers on both sides. Other exhaust lowering systems also would allow for this. This avoids problems of overheating which can sometimes occur with cut out systems.
On an 1150GS using the balance system along with the largest of the panniers the overall width is 98cm, the same as the handlebars.
Design features include a very efficient mechanism which does not require the pannier to be unloaded for fitting and removal. The panniers can be taken on and off very quickly.
I've used a variety of other systems before finding the Metal Mules. I have the Fat Mules and the large top box. The following are points I particularly like about the system.
1) Very strong build. Excellent low speed crash survivability (compared to other systems I've used). This is because of the angled corners and the inverted base.
2) Extremely easy to use, fast to take on and off and very easy to carry when not on the bike. Even with a tent strapped to the top the pannier can be carried using the side handles.
3) Flat top on panniers means your coffee / screwdriver / helmet doesn't slide off if you rest it there. It also makes for a comfortable camping seat (the rubber feet prevent damage to the base even on gravel)
4) Pannier lids don't come off completely so you don't have to worry about finding somewhere to put the lid when you open the pannier.
5) There is enough room to get your key in to the seat lock on an R1150GS without removing the pannier.
6) Panniers stack well when removed. Useful when floor space is limited.
7) Fat Mules hold a helmet (although not all will fit) The top box is designed to take any helmet (including peaked helmets such as the tour-x)
8) With the top box removed you are left with a conventional rack which is great for bungee strapping things to. When not carrying a pillion a large roll bag can easily be rested across the panniers and the top box rack.
9) The system includes a shortening system for the rear indicators. This allows you to keep the original BMW indicator lenses rather than having to compromise the visibility of your signals with micro indicators as other systems do.
10) Customer service is excellent. Paul who runs the company is an experienced overlander so he understands the needs of bikers first hand. He's also very approachable and will always give you the time of day. Not always true with some of the larger manufacturers in my experience.
The only faults I have found with the panniers are that the locks are prone to shaking themselves open on rough ground if they are not locked with the key and that if your bike lives outdoors water collects in the top handle recesses and can cause surface rust on the handles. Both of these are easily remedied by remembering to lock your panniers and a bit of wire wool from time to time. They are also prone to cross winds, but no more so than any of the other systems I have used.
EDITED for current information 18/7/06
I saw Metal Mule at Garmish and got chatting to Paul (nice guy BTW). It turns out that one of my complaints about the Mules has been addressed since I got mine. The 'rusty handle' problem is a thing of the past as he now makes them with stainless steel. A manufacturer who listens to his customers, what a refreshing change