Here we have a modified (Improved Design) this is more suited to the larger person, Longer Arms and Longer legs than a child. Not with excessive weight I would rate this as being suitable up to 100 kilo
After all it is still basically a child's bike, Now getting down to basics or modifications to the original Raleigh Twenty design:
Brakes originally had canter lever type which I personally never had any problem with, but a lot of people seem to find them inferior to V brakes.
Head Post steering changed to incorporate front suspension, and a longer raised handlebar
Top Tube lengthened for extra knee clearance from handlebar
this also gives more clearance from pedal to front wheel
Gears 3 speed improved to 6 speed with a derailleur changer
This gives a basic Idea of the possibilities and Improvements that can be made.