Will any lawn mower blade work properly on my mower?

As long as it's the same length and bolts up the same your good to go.

As long as it bolts up tightly and aligns onto the shaft (some have splines, some are hex, etc.) it will work. Will it work properly/as it should? Not necessarily. For example, a mulching blade isn't going to mulch without the correct baffles under the deck. Generally speaking though, you should be fine.

I just buy a new one when the old ones get dull. frick sharpening and balancing a $15 piece of metal