I have a Scott on mine too. There are the advantages and disadvantages to it. Adv : you can get a large reservoir for long trips that can hold a fair amount of oil so u dont need to worry about using up the extra bag space to hold a spray can. Another is that it carries a detergent, so when it rains, it sort of washes your chain for you. Also if you are terribly lazy like me, you can forget about it for a while - you just have to get used to the mileage and when you need to top up the tank.
Disadv: yeah it can make a mess of the back wheel, but that may be due to too fast a flow of the oil. I took off the sprocket cover the other day during my 6 hour clean and found a whole load of gunk in there that may have been there for 3 years (bought the bike 2nd hand), so it will be nice to take a look in another 6 months to see what is left behind. Blockages can occur if the nozzle gets burnt by the chain so it is best to keep an eye on it.
Overall, i think it's a good addition although nothing beats a good wax and some bike stands (or a main stand if you dont mind the additional weight.)