I have used and continue to use purple up in some systems.. with great success.
My preferred method of using it is in a reverse osmosis make up reservoir. it will saturate the ro water with minerals and when your system is topped off, it provides mineral rich water to the system thus reducing (somewhat) the need for ca reactor, two part or kalk additions.
Op, your bottle sounds fine to me..
In systems where low nutrients is the cause of low corralline algae growth, this product won't help, but if low magnesium (or another mineral deficit) is the problem, it may very well help..
Like any product, it has its applications and should not be just tossed in the tank and "observed".
If used, it should be used in measured amounts and your water should be tested for its possible effects on calcium, magnesium, ph and alkalinity.. and maybe strontium as well..
I don't believe it is snake oil.. It is fairly benign and not very powerful as a mineral addition compared to ca rx, kalk or two part so it is often thought of as useless by reefers who try it, see nothing and then disregard it..