This is the trans on the bike in video above it has dual chains between input and out put shafts with a 3:1 ratio,
I've been beating on that bike for over a decade and my nephew before that,there are metal covers and pull starters and hop up parts even for the cheapest version up to full blown race engines like SMB showed around 12hp.I've seen them used in mountain bike frames with a jack shaft to the gears on wheel and one young guy on here a couple years ago had one direct drive (single gear) with a 24" wheel.They are again cheep engines but setup and treated right they work pretty well but yeah they need to unload to get into their power range,and they will rev high with a pipe.
The nice thing is that transmission and the 7X one both bolt right up to Honda GX31and GX35's and they generally sell for about $30.
I'd like to find a 8H big sprocket in a 70 to 80 tooth count, but I've found none so far. The twin row chain version come with some pretty old and stiff reddish grease. I think that one thing I'm going to do down the road is add a little 150# gear oil to the chaincase as the drag from that grease is pretty bad.