A bit like all those fake round £1 coins that flooded the market before the 12-sided bi-metal ones were designed to combat forgery. Apparently 3% of pound coins in circulation were estimated to be forgeries at one point.
Thanks. Your latest pictures are much better, and I'd say your coin is not a problem - it's struck slightly off centre, but that's not unusual for early milled.
I agree - it looks kosher so probably a misdiagnosed denomination. But I'd say $150 is still B bit on the steep side for the most common 2/6 in the series.