#1... Yes, it's worth it IF
you just want to speed up your coralline algae growth at the risk of maybe overdosing your tank on one or more elements. Purple Up is a cocktail of different additives so you can't accurately gauge how much of what you're putting in your tank, especially if you're already dosing with other bottles of single elements.
#2... It's gonna end up costing a lot more than $14. You have to keep using it for a while to see results.
#3... Does it really work? Yep. I have 4 SW
tanks and I've been using it in 3 of them and after a couple months I can tell a difference in the amount of coralline algae between the tank without and the tanks with.
The most noticeable tank has huge spots of purple and green all over the glass and the walls of the in-tank fuge after only 3 months of being set up from scratch. Of course, I also started all my tanks with fully cured and aged LR
that already had colonies of corralline growing on it to get the party started.