VegasTriker

I've never seen this bike up close but was pretty impressed by the 19 pound weight listed in the specifications. That's a great advantage to a child over one of the obese bicycle shaped objects sold by mass merchandisers. One possibility for prolonging the usefulness of this bike would be to later add a longer seat post and add a stem raiser to the handlebars when your son gets taller. Both are inexpensive and easy to install. That would raise both the seat and the handlebars at the same time while still allowing him the reach the ground firmly.

I think your concern about the chain being "to close to the ground" is overblown. Chains are pretty tough. Think of the pressure a large adult puts on one when they stand out of the saddle and pedal up a steep hill. The rear derailleur is a bit more fragile but even those aren't damaged all that often. I've only replaced two in the past 20 years and one was the result of a rear light coming loose and falling between the chain and rear cluster.