My yard is pretty small, so I actually find it easier to use than a heavy, gasoline-powered, rotary mower. I can mow my front yard, which is about 1200 sq ft, in about 20 minutes.
Blades of grass are left standing.
Even with perfect technique, a few blades of grass will be left standing. When you see a yard that looks like that, stop and congratulate the neighbor on using a reel mower!
Sticks stop the mower.
A powerful rotary mower can mow right over sticks, crunching them into a pieces that fly everywhere. With a manual reel mower, even a very small stick will stop the blade. You must pick up sticks before I mow.
Leaves don’t get mulched.
A reel mower rides right up over a thick layer of fallen leaves, so I have to rake about once a year. With a rotary mower, you can just mow over leaves.
Tall, wilted grass isn’t cut well.
My grass has never gotten too high for the mower to not work at all, but I am definitely motivated to not let it get too high. If the grass becomes very long and wilted, it will not stand up for the mower to cut. A rotary mower functions like a fan and sucks up wilted blades.
Obstacles get in the way.
If your yard is full of bird baths, figurines, small trees, playground equipment, etc., then a reel mower is probably not for you. The mower really only cuts when it is moving, which can make it difficult to mow around a lot of obstacles. With my mower, the blade keeps spinning after I stop pushing, but it is pretty difficult to use that feature to “cut in.”
Mowing is more work than just walking.
I walk a lot and bike some, but I’m not really an athlete. (I only run when chased.) I have no problem mowing, but other members of my family have complained that pushing the mower takes a lot of work. You could cancel your gym membership! Technique makes a big difference.