Several times (through neglect) my synth got a film of dust which is not a good idea. The Decksaver offers protection from dust and fluids, it fits perfectly, and I'm delighted with it. The fact that it's a clear moulded plastic means that it also happens to be aesthetically pleasing.
Cons - none. However, I bought one for my Drumbrute that doesn't fit properly and it rocks back and forth, so there may be a few duds here and there.
I'm trying to buy protective and/or functional equipment such as this which is not as exciting or interesting as an actual synth or pedal, but is important and makes music creation more pleasant, safe for the gear/wallet and efficient in the long run.