It's true about pollution and mileage. As I said 4 strokes kits do have advantages. Reliability ain't one of them. Show me a single link for a 4 stroke that went 14k miles or even half that.
You asked for it, you got it. From this page at a competitor whose products I have used and respected:
Staton-Inc motorized bicycles bike kits and gear drive kits.
"We have current customers who have more than 50,000 + miles on our kits (gear box and rear custom hubs) and they are still running strong since 1984. The Robin - Subaru, Honda, Mitsubishi & Tanaka engines are rated for 600 + hours of use. We have had many of these engine run 2 & 3 times the rating. Engine life in miles. 600 hours @ 30 mph = 18,000 miles. Your engine could get as many as 54,000 miles or more."
Even the best 2 strokes will find it hard to match that. Why do you think the auto makers gave up on 2 strokes before most reading this forum were even born? Long before we even had an EPA or emissions laws. The 2 stroke's biggest failing is the very thing that makes them appealing to many riders-- the power band is at or near the engine redline. That means that to get the same amount of power to the wheel at any given RPM the 2 stroke has to be geared lower and wound tighter. And keeping any engine wound tighter will cause it to wear quicker.
And for those who think 2 strokes require more maintance... Yes, the 4 stroke does require the occasional valve adjustment though I've yet to adjust my valves in over 5000 miles and I do take 10 minutes or so to change the oil every thousand miles or so.