I have no idea about the shelf life or the usage rates for this ingredient because I can't find a data sheet on it anywhere. I have found a few things here and there, but I've written to Voyageur (where I bought it) for more information. It is water soluble, and I have been using in toners at 2% so far.
The main claim is that it contains anthocyanins, which are water soluble flavonoids that give colour and protection to plants. (They are anthocyanins when they contain a glucose molecule, anthocyanidins when they don't.) They are very good anti-oxidants, scavenging those free radicals that lead to rancidity and spoilage. Acai is reported to have very high levels of these anthocyanins - that's why they keep calling it a superfruit - but again, I don't have any information for this specific product. It is also considered astringent with good burn and wound healing qualities.
If you wish to use this specific version of the extract, it is water, alcohol, and surfactant soluble and suitable for products with a pH of 4 to 12. It is used in the cool down phase of your creation. If you want to make anhydrous products containing acai, you'll have to get the oil, which is filled with phytosterols and omega 3 and 6 fatty acids!
Is acai really a superfruit? Well, that's not really my area of expertise, but I can tell you that it compares well with blueberries on the nutritional front (my favourite!!!) and it seems to be popping up in everything from tea to chocolate to cosmetics. (Combined with blueberries, which is very annoying because no one ever wants to leave blueberries alone! They're always combined with pomegranate or acai or some other superfruit! Let blueberries shine as the star of the show!!! Sorry, I just love blueberries!)
Join me in about an hour for my toner with this ingredient!