I used to use Flourish Pond Tabs until I couldn't find them any more. Seachem states the contents of their products very clearly so it shouldn't be difficult to compare the two. Chances are they are identical just more concentrated. Obviously a small error in dosing the more concentrated product would have a greater effect than if you were using the normal product, other than that I don't see a problem with it. But check the contents as they could differ in some ways. Otherwise just try to be more precise in the doses to avoid any problems.
Hope that helps