Things to consider in these three bikes:
2 are metal, 1 is wood.
The seat on the Runners has a foam padding.
We've never had a return on any of the three models.
The Strider can have an extra extension pole added to it make it taller (sold separately [Strider SPORT now comes with 2 seat poles]). You can also get a Ski set for the front in Winter to convert it to a single Bike/Ski.
They all have 12" wheels but the Kazam has a higher seat than the Strider which is ultimately better than having to get the extension pole for the Strider in the future as the bike is bigger overall.
If you wanted a honest recommendation I would recommend the Kazam, Super 16" Strider or Go Glider Bike for a 4 year old. If he is normal/tall for his age the Strider and Runners will already feel like they are getting smaller for him and the Kazam, Super 16" and Glide Bike will be better suited for his age and last longer. Our 4 year old just got a bike with 16" wheels and it's big for him but not too big.
Measure his in-seam and that will help decide the best height.
The Go Glider seat starts at 16"
The Kazam seat at 15"
The Strider Super 16" seat at 17"
If he hasn't biked at all before the Kazam is a good choice or the Go Glider but if he is strong and confident the Strider Super 16" is a very cool bike.
Strider Super 16":
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