I've got two of them- they are cruiser frames with 700c wheels- and they roll and perform well, and still pedal much like a normal bike. One is a 66cc and one is a 50cc.
If you're not going for pure speed, the 50 cc is actually quite capable for city/urban transport- and usually more legal. I can get 20 mph easily which is quite handy with baskets.
I've been waiting and pushing for years for a 33cc China Girl for lighter touring frames- never going to happen, but the bikes in my opinion had really caught up to the motor in lightweight and rolling potential before they put out the 66 motors. The 50ccis considerably more quiet and has less vibration- a 33 cc would be even more so.
If the bike is set up- fast rolling 700c can be ideal but I think the main idea is to stay thinner than beach tires. I push the narrow a bit because I got plenty used to sew-up tires back in the day, but the bike is heavier and so am I, yet the roads are sooth here. Something like 28 or 32 mm - and maybe mixed with a heavier rear, but anything under 35 mm is a good roll and will save weight.