Coincidentally, like GW I too have a motor loc - on my BRe Honda 5.
Similar fitting issues i guess?
It's a very snug fit within the hulls motor-mount recess. Not a problem as mine stays in place all season, hence I see this as a security advantage!
Easy on, easy off?
Can vouch for this item, I've had several over the years (boat changes...not thefts!). Very well made, high quality. Works well. Secure. No rust, either externally, or in the lock mechanism.
I have the small square version too, on my tenders Honda 2.3. the motor on that also stays mounted all season, boat being left on the beach.
IMO, you'd need to do some significant damage (cordless grinder/sabre saw?) To get it off.
I wrap the motor toggles in fingers cut off "examination gloves" so as to prevent rattles inside the lock body.