THing is, some of the blades can last through wacking weeds along those rough, keystone shaped POS concrete blocks that people build retaining walls out of. $2 of the right bladetm will outlast $2 of string and you will never have to stop and screw with it. Ever. And changing the blades take like 30 seconds total, with no tools. I tip mine up sideways and clean the grooves in the concrete walkways and do light edging the same way.
Ah - just went and got the blade package. "Grass Gator" - just the bestestestestestest. est. I will paypal you $35 if you try it and don't like it. With those blades. HEad is $15, blades are about $9. It would be nice if you would send it to me in that case. Thus the extra $10-ish,