I have bought numerous different plastic full-cover cases for the N900 between £1 - £10, and all are the same - they break after a month in some way, usually the top cover just falls off. What do you expect?
Not with this one - Instantly I know this is going to last, I can't take off the front bit now without the plastic wanting to warp slightly, very reassuring as it doesn't even do that easily - the pieces are much thicker and lined with rubber, to grip the phone better. It couldn't form a better fit.
Every port is accessible, and the buttons on top are even nicer thanks to the rubber again. I hate this stuff over the whole phone as it feels slimy and gathers pocket dust, but its useful when its on buttons, as a "feedback" that "you are on the button!" ;)
No point in getting anything else, those leather cases are nice but you can't use the phone in any way without taking half the case off usually. This one is no fuss - it looks good without looking gaudy, feels nice and the general quality feels like it'll last as long as the phone. Best of all everything you could do on your N900 without a case, you can do just as well with this on - you only need to disassemble it if you want to get to the battery/SIM. Every other function works, even the IR transmitter/receiver has a window!
Buy one now, you won't be disappointed! Don't let the slightly-above-average-for-plastic pricetag put you off!