Had a fun few games with oil springs. As far as a physical product goes, well
worth it. Tiles look/feel like the games ones and the rule changes are explained
in detail.
After a few games I'm thinking I may fiddle with the rules. Oil seems too
flexible. Everyone ended up just grabbing some oil and converting it to
resources instead of trading.
A nice bit of flavour if you only have standard Catan, otherwise if you've
got one of the expansions, I wouldn't bother. I no longer use oil springs
after obtaining Cities and Knights.
For the low price, it's worth it to spice up your next game.