Highly recommend getting one of these every summer or two.. It's worth it not to wait until it wears down to the guide holes.  I almost forgot how good the edger worked and how much quicker it goes if you have a good blade.  I think the blade I just replaced was around 4 years old or so.  I have a corner lot with angled sidewalk at the curve so you can tell my blade tends to wear going around that area.  I just wanted to comment on the design of the blade that concerned some people.  Not sure why they have the wrong picture above but the center of the blade is a circular hole.. and this is a good thing much like a circular saw blade.  If it was angled to grip the shaft you would risk causing damage to the shaft or stripping if you catch the blade on something.  There is no slipping of the blade if it's tightened properly.  I didn't even bother to use a torque wrench.  Just a quick half turn to tighten and it's good enough.  I highly recommend this product and it is worth the price even yearly (though it will last much longer) just for the satisfaction a new blade edging produces.