I never found the need to lock my scooter seat.
Sure - if I have an 'off' I'll be picking up MoonPies and a couple of tools - but I figure I'll have other concerns if that happens.
My Piaggio seat takes a right shove to latch it - so it's almost never latched - has a fancy electric button to activate it on the headset....which I use so rarely that I forget it's there!
There's a back-up manual lever behind the locked glove box door.
The LIKE200i seat latch works fine - and has a very short cable since the side panel key hole is near the latch. I don't often ensure that the seat is latched. I've rigged a line to use for emergencies.
I've secured a key on each scooter - accessible with the mini Swiss knife always in my pocket.
Scared myself one very cold morning miles from home - when I was ready to head out.
I had dropped my key inside my rain pants....not in my pants pocket. The rain pants have an elastic cuff - which is where I found them!
Went home and hid a spare key on the scoot!
Stig