It may not surprise some folk that the back of their mower blades become much sharper than the cutting edge which bluntens very quickly when hitting stones or mowing in sandy areas. The better the quality of blade the better the up suck of the flutes and the quicker the wear.The longer or rougher the work (grass instead of lawn eg paspalum stalks after cut can become like steel as I discovered as the previous contractor cut way too high to save time). Like grinding/cutting discs, blades tighten (usually) as they are worked. Too long to go into the "usually".
One can't legally hardface the cutting edge because of non insurance payouts and expensive legal costs to boot.
After much difficulty in removing blades for sharpening or replacement, and a couple of times receiving nasty cuts, to the inside of my fingers, from the jagged razor like backs of blades, I tried gloves which were near useless (riggers cut also & welders ones were too time consuming & clumsy.
Often I had to apply much more leverage than a 12" or 24" shifter could deliver so this tool was devised.Heat can't be used due to seals and the conical lock washers (as on Kubota decks).
A short cut in construction actually proved to be better as I used blades with no step, average step & a deep step depending on terain and possible onlookers or pedestrians/ car traffic etc. The short cut was simply welding the gal tube against one edge of the RHS. It was simply easier to do.
The length of the handle allowed it, once the RHS was slid over the blade, to be jammed against a deck hanger(ok) or mower wheel (best) when blade bolts were really stubborn (otherwise held in one hand). At the stubborn point, the loosening tool (3/4" ratchet wrench) could be held with both hands and the body perched against something solid like the rear wheel of the tractor or the mower trailer in the field. If even more resistance was encounted, then pipe could be slipped over the wrench to gain more leverage.This was always enough with kubota decks and those of shibaura.
With my 6 ft John Deere deck even more leverage was sometimes required so the mid mount deck had to be removed and turned upside down.
This allowed even longer pipe to be used for leverage. The reason that the Deere was more difficult was that their bolts "grew" in length sometimes way more than 1/2 inch.
As long as I have a ride on or tractor mower I'll keep this very simple tool. Saves fingers, frustration & energy.