Talking key-start, I had a John Deer JS-48 self-propelled for a short period.
This mower was a beast, it had the HP version of the 190cc OHV Briggs, the thing ran hard and would often have fuel cracking off into the hot exhaust when shut down. The self-propel system was variable "personal pace", lean in to the handle and it would take off, the harder you leaned, the faster it went. These mowers could mulch, catch or side discharge. The key-start was nice to have too.
I had to get rid of this pretty quick. Being an American style mower, the deck would not go low enough and half of the rear discharge shoot was taken up with the gearbox. Americans tend to have quite tall lawns and generally use a mulching mower to take the very tips off each mow. At this, the JS48 was excellent. But for Aussie lawns, it just could not effectively catch lawn clippings on our preferred lower cut heights. Both the rear and side discharge shoots were to small, blocking them up frequently and bogging the engine down until it stalled.
In the end the time I saved with its wide cutting width and fast ground speed were was wasted with me having to clear blockages far too often. I really wanted to love this thing but I gave up and bough a Rover ProCut instead.
I think my experience was echoed by many others because these things are no longer for sale.