I looked at your Saffron link, that in the UK.
I hunted down a similar product here in the US:
That looks like Iranian saffron rather than Spanish. I have not really tried Iranian; it may be just as good, but I've always used Spanish.
You can also buy saffron in capsule form from supplement sellers. I have not yet tried this as a comparison, but I assume it would be genuine saffron.
The saffron sold in UK supermarkets also appears to be genuine (when I tested some supermarket saffron using the fake saffron test, it came out as legit). But supermarkets tend to give you a small amount of saffron for a highish price, so it is not the most economic source.