An example of a Propin is:
http://www.pinpics.com/cgi-bin/pin.cgi?pin=4526&sid=8480.1197939098.v2
This is a pin I have, and happy to have it.
But this is a smalllll pin. (3/4")
Normally they are not even that small. But Propins are generally smaller than a pin you buy at the park. They are often approx the same size as maybe a cast lanyard pin.
The coating will also be a clear epoxy like coating. Which can be a plus because that coating is very durable. Howver many yellow with age, over a long period of time, as in several years.
Many (if not all

) Propins are part of a set. I don't know if all sets had 9 pins. But the sets I saw did.
The plus side to Propins is they often had the charcters not often seen. That is one thing that made them fairly popular. That and the price. The artwork was generally different poses than Disney park pins too.
Here is a link to a set of Propins.
http://www.pinpics.com/cgi-bin/pin.cgi?pin=9377&sid=8480.1197939098.v2
They were pretty cheap, and often people broke them up and had 9 traders.
Unless it is a character or pin you like, I would stay away from Propins and the Spain pins in general.
Actually even another Propin I have that I would probably never consider trading is:
Pin 4979: ProPin - The Lion King Set (Rafiki in Yoga Position)
http://www.pinpics.com/cgi-bin/pin.cgi?pin=4979&sid=8480.1197939098.v2
So they really had some nice pins. But again if it was a theme you cared for.