Last spring I bought that 40 mm filter from 2filter. I've been very happy with it. I also have the hood/filter combo - two of them as one filter (the ND or the polarizing one) is now permanently attached to the adapter ring. Anyway, the X10 is pretty rugged and I usually use a neoprene wrap "case" and toss in in my purse. For cycling and travel, I used a BlackRapid case that attached to the camera strap (I forget what it is called) but it keeps the camera protected and then you just slide the camera out when you want to take pictures.
Anyway, the only reason for the hood/filter was because I had trip to Iceland and Greenland in June and had wanted to be able to stop down a bit more. I didn't use the filters very often and when I didn't need them just relied on the Marumi filter on the camera.