$680 w/shipping is an excellent price for the AMS (Infiniti-branded) HE. I got mine for $629 after discounts, which was $729 sale price + 20% ($100 max) ebay discount + free shipping, back in 2017.**** , i literally just pressed buy on AMS HE that has the Infiniti logo on it for 680$ with shipping ... and thanks!
I will note - the only issue I had with my HE installation at the dealer was the shop foreman slightly overfilled the HE reservoir (which is better than not enough coolant, right?), so the IC Coolant was burping out the overflow. I quickly realized that, waited for the engine to cool down, and then I used a turkey baster to draw down the level to between the MIN/MAX marks. No issues since.