Re: lt 50?
My son has a Kasea mini 50. We've heavily modded it. Will do 22 mph with me on it. My son is 5-1/2, 44" tall and @45 lbs. He flies on it and the rear hand drum brake stops him fine. I paid $1100 in NJ and I have less than $150 into it.
I never looked at the Suzuki, b/c the older model was a pull start. I'm not sure how much the new Suzuki costs. Either way, if you want him to race, anything you buy now will probably be only to get him started and learn to ride. Once he's about 5-6 years old, you'll be looking at a full youth size Kasea SkyHawk 50, DRR 50, LEM (although the LEM is small and very light... it will cost you a fortune and a good welder to be a racer), Eton 50, etc.....
Rest assured though, if you buy a micro mini, you'll have friends, family or neighbors lined up to take it off your hands when you're ready to move your kid up to a full size youth quad.