If you want putting green quality grass forget this idea. It does not produce a manicured look. It looks just like grass cut with a regular mower after a couple of days growth. See lawn picture in the gallery. Try it yourself first with your weedwhacker to see the results. 

I only spend 1/4 the time I used to spend cutting grass now. Twice as fast to cut and then only half as often.

The 7" grass looks a normal length from the road. It's the uneveness of long grass that looks bad not really the length. This mower just clips the tops to make it all an even height. You don't have to worry about running over and hitting the power cord as 7" is far above it. 7" is also higher than small flowers present in the lawn. Much better for the bees. 

No Mow May is a thing. Save the bees. https://www.cbc.ca/news/canada/toronto/no-mow-may-toronto-1.5568446

Cut your lawn 7" high all year and preserve the small, low flowers like violets. Not just in May.

The issue with letting grass grow very high is standard lawnmowers can't easily handle it when you decide to finally cut it. Standard lawnmowers stall out and create large clumps of cut grass that need to be raked and removed if you try to cut really long grass. Not an issue with this one. 

In areas where grass refuses to grow plant a wildflower mix and enjoy a large variety of colourful flowers, along with the bees and butterflies. Manicured lawns are boring and not natural at all.

How far the roots go down depends on how high the grass grows up so 7" grass is much more drought tolerant. I don't water at all. Stop paying sewer charges for water that doesn't go down the sewer.

Anything you do to help grass grow like aerating, watering and fertilizing also helps weeds to grow. If the surface of the ground is dry and rock hard weeds can't start. Existing ones die at the next drought.

Plant Ecolawn and forget about most lawn maintenance. https://www.wildflowerfarm.com/index.php?route=product/category&path=20

This year (Aug 2021) I've only cut all of it once, so far, due to the very slow growing Ecolawn. In spite of a lot of rain. People spend far too much time and money on grass. Let alone the constant noise from mowers and leaf blowers.

 Longer grass collects more dew overnight. It spreads faster as well. I used to have many bare patches. The wheels are mounted behind the weed whackers so they don't trample the grass in front of cutting it. Much easier to push around than a push mower since it's only 20 lbs. A single 15 amp outlet can easily power three 4 amp 12" corded weed whackers. There is 1" of overlap. The middle one is held with wingnuts so it is easily removed if you want a single weed whacker. 

String advance is automatic. It advances a bit every time you turn the motors on and snips a tiny bit at the end. If you don't run into anything the cutting string lasts a long time. Just cutting grass doesn't wear or break the string. I am still on the original spool after 6 years.  If you do run into something hard and break it you can hear the rpm increase so you just unplug and plug the motors in again and it advances.

Weed killer is illegal on lawns in Ontario so most people have to put up with dandelions and other weeds. Taller grass is a much more environmentally friendly way to eliminate weeds without any effort or cost. Short grass full of weeds, in particular dandelions, like most of my neighbours, looks far worse than weed free, 7", even length grass. 

It seems people cut their grass really short in the spring to get rid of the sight of dandelion flowers. Really bad idea. That just weakens the grass and encourages more weeds to grow and it leaves most of the dandelion plant behind. People who spent thousands on sod now have a lawn that is bare or mostly weeds after only a couple of years. I am also not a fan of dandelions. To get rid of the odd dandelion just push a pointed spade down beside the stem and lever a bit. Now grab the stem and you will get almost all the root as well without leaving a big hole in the lawn. Once they are gone there is only the odd one every year after that.

In 100% shaded areas where it was mostly bare with yellow grass I encouraged moss to grow. Moss has no roots so to encourage it you need to keep the surface moist with a couple of minutes of water mist every hour. Most water timers can't do this many very short cycles so I built one with a controller.  https://hackaday.io/project/171942-two-zone-wifi-water-timer

That is one of many $$$ saving projects at https://sites.google.com/site/nodemcu12e/. 

Now the area is bright green year round and no watering is needed. Zero mowing or any other maintenance. I use the single weed whacker to trim the few blades of grass remaining in the moss very close to the ground. I actually let the center touch the ground and sweep back and forth. You will kill the grass without touching the moss. If you have weak grass and you can see moss this step will reveal it and green up the area.

 The only time I use the gas mower is late fall so the grass is short over winter and not matted in the spring. I could modify the design so the cutting height is easily adjustable over a large range and not use the gas mower at all.

I have been using this mower for the last 6 years and the grass has never been better. 

It used to take me 2+ hours to cut the lawn with a 21" self propelled gas mower every week. Now less than 1 hour every 1.5-2 weeks. The first cut was not until June 1. Very little in August usually so less than half as often. 

So only about 1/4 the time cutting grass now and it looks much better. Long grass looks thick even in spots that are actually thin.

It used to be I had to cut it before it got too long or else the gas mower would often stall and leave clumps of grass that needed to be raked and picked up. 

Now it doesn't matter how long the grass is when I cut it and it doesn't matter if it's wet. Very little of the cut grass is visible on top. Most of it just falls between the long grass blades. The picture of the lawn is right after cutting 3" or so off the top.

Black and Decker 12" Single Weed Whacker Lawnmower for small lawns.  https://www.youtube.com/watch?v=zep1WzLJ3Ig