Im turning a bit skeptical about this

The hard puzzles are really nearly impossible to solve within a reasonable time frame. I highly doubt that at this difficulty level the puzzles would help you achieve anything in chess.
Complicated Puzzles that take more than 3 minutes on average to solve are useless for the blitz player.

I also bought the intermediate 350 mate in two package, and most turned out to be mate in FIVE!

Not good.

abedzaza about Chess Tactics Pro (Puzzles)