If you decide to buy Mammoth P (not saying you should or shouldn’t), get it at a grow shop so you could check the expiration date. I read many reviews on Amazon complaining about expired bottles (same goes for most bacteria/fungi based products on there). I’ve also heard it should be a light golden color and you should avoid it if it looks too dark. Greencoast sells it in our neck of the woods.
Edit: Reading the Mammoth P FAQ, I see that the date on the bottle is the manufactured on date (not an expiration date) so I think those reviewers might have been confused. According to the website it will be good for a year after opening. And yes, the color change or any sediment/floaties seem to be normal.