I know them well. Too well, in fact; they're on my "never again" list. They are smooth and fast, as you say, but the 16" ones on my commuter bike never lasted more than 700 miles or so. 20" one on the tandem lasted maybe 1200 miles.
And they are also pretty light.
Seems to be the trade off for performance... same thing happens with high end road tyres and smaller wheels wear out 1.4 times faster than 700c tyres of the same design..
Have some 27 inch Avocet TT30's that weigh nothing, and are as fast as sin, but are probably only good for 500 miles.
Friend gave me half a dozen Primos the other day as he does not ride 20 inch bikes and have been running the front tyre for many hundreds and hundreds of miles and it still looks great but all the load is in the rear.