Hiya.. Elay - that's not the stuff that I've bought.. I think there are a few different things people get.. either:
-husks (look a bit like a light brown readybrek, or wholemeal flour, and are literally the husks of the plant, gound up a little bit, but not into powder)
-powder (the ad you linked)
-capsules which contain the powder
I wanted the husks cause:
-that's what I have seen recommended
-I wanted something to mix into the porridge and make it more enjoyable (which it did)
- can't explain my third reason, but it's something about slightly trusting the husks to be what they're supposed to be, instead of some random bleach-white powder which could be anything...
Of course, this is just a personal preference, and I've come accross people on here who swear by the powder, or who get the capsules, and open them and add them to food...
Psyllium Husks ..
This is what I've bought, and i guess it'll last for months in the amount I'm going to be adding! (didn't buy it from this shop.. bought it at a health food shop called G Baldwin and Co.. all look the same sort of prices though.. 250g bag for a fiver-ish, up to a 1kg bag for 18 quid...
Hope that helps!
Vx