The thing with say a Specialized HotRock is that you can recover the cost. The Magna is at best a single-use bike which will have to be disposed of after a season of riding. If you're lucky, the child will outgrow the bike before it completely falls apart but even then the bike will probably be left in a fairly unusable state. A HotRock can be reused and/or resold and you can recover some of the investment when the child outgrows the bike. Amortised over time, the HotRock is a much better investment and will give you less hassles during its period of ownership.