Not long after I bought mine I pulled into Vine's of Guildford and the chief mechanic spotted them and said "two things about Metal Mule, they restore your faith in British engineering and they are the only accessory I can think of that is more expensive than the BMW option!"
They are certainly not cheap but they are tough as old boots and if you are into serious adventure riding (Long Way Round in 2009) you don't want to spend your time welding up frames and bashing panniers into shape when you have the inevitable off. They come in 31 and 38 litre versions but the price is the same regardless of size. It's tempting to get "more for your money" but my recommendation is to go for the 31 litre panniers otherwise you will just pack more stuff that you wont use/don't need! The anodised version is the one to go for as aluminium dust in your underwear is not recommended!
The construction design makes them incredibly strong. An altercation with some very low flying geese in Canada resulted in one of our team laying his bike down at around 100mph. The ally on the right hand pannier is no longer 2mm thick(!) but it is still fully waterproof and went straight back on the frame without any bashing or bending.
The attachment mechanism is very effective and the time to take off or put on a pannier is all of four seconds! For pannier liners you can't beat Waitrose fabric shopping bags which they give you free if you use their in store scanning service! Pefect fit and they come with handles - marvellous! Paul Goulding the owner and designer at MM has done a lot of touring and is a veritable mine of information and not just on panniers.
Value for money? If you are serious about adventure riding and want one less item to worry about then it's Meatl Mule for you.