Is This German Guinea Coin Authentic?

I have one of these which I know for certain is genuine because I can establish the provenance back to New Guinea, before WW2. The coin in my possession has been a family heirloon for more than 90 years.

Looks generally OK to me, but I do have a couple of questions that need to be followed up.
1.) Ring test. Rest the coin on the tip of a finger and gently tap it with another coin. Compare the tone with another German 5 Mark piece of the same size.
2.) Weigh it. Should be the same as any other German 5 Mark piece of the same size.

I don't have much of a problem with the displaced rim denticles below the Bird of paradise on the reverse. That displacement could be the result of adjacent edge bumps, but that those areas should be examined more closely.

How much did you pay for it, and do you think the seller had a good idea of it's value? Also, do you have an idea of it's value?

I must admit, I got a bargain without realising it some years ago.
I bought a 1923S Standing Liberty quarter in nice VF for $3! I knew very little about U.S. coins at the time. Apparently, that applied to the seller as well!

The reverse design of this coin must rank up there with the Liberty Walking and the St Gaudens coins as the most artistically merited designs to be put on a coin.

That helps to explain their market demand, hence value.