I've never seen the one you are asking about - but a company called Sea Labs sells a line of these slowly dissolving blocks for a variety of purposes.
I have put one or two into my system to see what they would do -
They slowly disappeared, but I didn't notice any difference. It wasn't really a fair test as I dose ALK/CALIUM anyway and I didn't use the number of required blocks for my water volume. (Doing so would be too expensive for a system my size)
I'm a bit skeptical - I guess they could prevent complete exhaustion of ALK - but I don't see how they could maintain a balanced system either.
If you want - you'll find more info by googling the sea lab products. Some people like them - others question their effectiveness. I couldn't afford them either way for my system.