The idea is long overdue. That's a battery pack on the left side of the reel housing. It powers a small motor that spins the reel. The gearing, however, allows the operator to provide all the power if he wants. So for thick grass, one engages the motor. For thin grass, one simply pushes.
The mower is the Mantis Cordless Reel Mower in the United States. Europeans would purchase the Brill ASM 380. (I looked at the builder's plate. Mine is also marked Brill ASM 380.) I got it on sale from Amazon. It's a smooth running machine, and under power it cuts quite effectively. I will have to invest in some additional battery packs in order to do all the mowing in one go.
In the States, the J. G. Brill company (no relation) built streetcars and interurbans, including the famous Brill Bullet cars. Look closely at the control station on my lawnmower. With the left hand, depress the red button and with the right hand squeeze the lever. It starts cutting. As long as you hold the lever closed, the reel turns. Release the lever, and the reel starts. You have to do the depress-and-squeeze routine to restart it. The deadman control handle on a streetcar uses the same principle. (Unlike a streetcar, however, this control stand can be set up for left-handed squeezing.)