The steel frame on these runs form about 8.5kg for the 12-inch up to nearly 13kg for the 16-inch, so they're sturdy enough to take a beating but not so heavy a 3-year-old can't muscle it around the driveway — the full chain cover is a nice touch we added after too many parents asked about pinched fingers.
We've sold these mostly to daycares and families with multiple kids, and what we find is that most buyers go with the 14-inch for the 4-6 year old range since it hits that sweet spot between the 12-inch being outgrown too fast and teh 16-inch being a bit much for a 5-year-old to handle.
The training wheels are removable with a single wrench (usually takes about 5 minutes), and the saddle has that spring suspension that actually makes a difference on bumpy pavement — we tested it on a gravel path once and it soaked up vibration better than we expected for price point.
Lead time is roughly 20 days or so if our company have stock, but the red and pink tend to move fastest so you'll want to confirm availability if you need a specific color for a batch order — the black and yellow are usually easier to keep on hand.
One thing that's not always obvious is that the foot brake version is better for younger riders who haven't mastered hand brakes yet, but the caliper brakes give more precise stopping power for older kids who are already comfortable on two wheels.