I have heavy clay soil with a hardpan about 12 inches down. When we first bought teh house (newbuild) I had to take a spade, fork, pickaxe and crowbar to it to loosen the soil, and then added loads of manure, sand and gypsum. I used my mantis to break down the clay lumps and mix in the stuff I added. It was great for this job, and saved me many hours of work. The tiller would never have done the job on its own.
Since then I have repeated the process as I have added raised beds and expanded the borders, and wouldn't be without it.It's very easy to handle / lift etc..
I used it on MIL's garden in her newly acquired home last year. Her soil is wonderful, deep loam, and the tiller went down 15 inches like cutting through butter.