Does anyone have complete spec on this thing ? 20" is NOT a wheel size, so in particular I'd like to know the tire size of the Urbano 5.

You can divine the wheel size by the tire size spec. A fractional size such as 20 x 1⅜" is ETRTO451 while a decimal size such as 20 x 1.50" is ETRTO406. In this case, it's the former.

Not real sure. The Urbano 3 is listed with a decimal number, the Urbano 5 with a fractional number. This seeming conflict is why I posted to see if anyone had one and knew for sure. The rest of the spec between the two is somewhat different too, the Polygon website was put up by someone without great technical knowledge and whose primary language isn't English.

FWIW I'd rather have 406 due to better availability of tyres. But, 451 would offer ( for me) a better ride.
I haven't yet checked to see if Continental Contact tyres are available in 451 and what sizes might actually fit an Urbano.

Polygon is an Indonesian brand that manufactures in the province next door, literally. That all makes sense.

Indonesia sounds much better than China. This could be why there are people who rave about how good the Polygon built bikes are.

I can't speak about conditions on the ground in China (PRC) proper as I've only been to Hong Kong and Macao (and the other China, Taiwan), but I'm pretty certain Chinese manufacturing has now surpassed Indonesia's in quality and tech.