OK, 1st and 2nd hand information here...so gimme a little slack. I HAVE the Katadyn. It's the BOMB. Ergonomically, it CAN be a little fumbly, but once ya figure it out, and/or use the fast connects to fill a hydration bladder, it's a breeze and a joy.
Now, as for the MSR...I HAVEN'T used it personally, but the folks I've talked to (and at REI before I bought the Katadyn) told me that there were two problems with the MSR...the handle would break and that easy to clean ceramic filter will crack or even shatter if even barely dropped on a hard surface (dropping not uncommon with cold, numb fingers in Colorado mountain spring water), rendering the filter useless. Again, 2nd hand info, but one was a customer and another was an REI employee...both replaced the MSR with the Katadyn.
Hope that helps just a little.
OH, one more thing...make sure you purge the things after filling your containers. The Hiker Pro will spit out carbony water next use if you leave water in it...but that's a good tip for ANY filter.