I'll try to keep this short and simple... Before I got the Worx mower I purchased the Black & Decker MM875 19" Lawn Hog (corded) - used it once - and returned it the next day. Not what I was expecting or hoping for... I purchased the Worx 13-amp 16-Inch Electric Lawn Mower #WG712 on Amazon. Right out of the box when compared to the Black & Decker it is better looking machine. The Worx is lighter and smaller making it a lot easier to use and maneuver. Yeah, it is only a 16 inch blade, but combine that with 13 amps (instead of the Black & Decker 12 amp motor on a 19" blade) and you get plenty of cutting power. I figure because it was so easy to maneuver around various landscape boulders and such, it ended up being just as quick as a larger machine.
The Worx height adjustment was well sprung and easier to use since it had a large knob that was right on top of the machine - and it is numbered - unlike the Black & Decker. In general I thought the Black & Decker was bigger and heavier than it needs to be making it harder to maneuver. The Black & Decker's height adjustment on the front side wheel wasn't very convenient and it wasn't numbered. Further, the Black & Decker didn't cut as short as I'd like. The Worx cuts down to ľ ". At 12 amps the Black & Decker appeared to have sufficient power - but did slow down on a number of areas on my lawn.
Looking at both machines from underneath, the Worx has a double-lined body that covers the blade area - the Black & Decker did not. If something was to go really wrong with one of these two machines, the Worx appears to have a stronger/safer build to stop debris from cracking the body or making its way through.
Another big difference between the two is the grass hopper. On the Worx it is hard plastic and hangs above the ground behind the mower - It does not drag on the ground. Pull up and back and it's off the mower. Dump the grass into a bag or trash can - bang on it to get all the all grass out, snap back on. It even has a little window so you can see how full it is. Very easy to take off, dump and put back on. The Black & Decker has a mesh bag that I found harder to use - just taking off and putting back on. Also, because it's a mesh bag when I went to empty the thing it tended to collapse as I tried to dump out the grass. Not like I can bang on it to get out all the grass, so you gotta' shake it out. Further the Black & Decker bag tended to drag while attached to the mower and based on the label sewn to the bag - it's expected that it will wear out and need to be replaced - The Worx hard plastic hopper looked like it would never wear out.
Overall cut quality is fine on both machines, but hands down the Worx is a much better machine for me. The Worx is lighter, more powerful, well built and easy to push and adjust - just easier to use, plus I'm helping the environment.