Absolutely love them. Came across them from a Facebook ad, having bought Waterdrop before.
They're delicious! Tastes like a Rubicon. My only (very minor!) complaint is that sometimes they tend to crumble in the tubs. And if you're using them to hit your water goal, they add up and aren't super cheap (if you drink 3l/use 6 cubes a day, which is *very easy* lol, a pack of 6 tubs lasts 30 days instead of 180 days)
That being said, they are definitely cheaper than the competition, and the packaging is so much better than Waterdrop! Waterdrop has a slide-out drawer with individually wrapped cubes, so if you drop it (been there) or it slides out in a bag, they go everywhere. GoalWater's is like a chewing gum tub (best way to describe it), which is brilliant as you can just chuck it in your bag and not worry (I have had the lid come off, but that's from repeatedly opening and closing it)
One thing I would love to see (apart from maybe some new flavours) is a recycling scheme (which I know would be quite complex to put into place) which might make it cheaper long term and better for the environment.
Zooki does something like that; with each order, they send a prepaid envelope (easier to do with sachets; not sure this would work with tubs) and any empty sachets are collected and sent back in the prepaid envelope (with order number/email written on it) and credited to the account with 10 sachets giving £1 off.
Better for the environment, and cheaper for customers; win-win.