You've posted this in the Players section mate, it should be in Tactics & Training. But yes they do work, but as the others have stated, your team is going to be different to theirs, no matter what. There are so many variables that you wouldn't even think of and one of the most important is consistency. If you download a tactic, try it for 2 or 3 games and it doesn't work, then try another tactic with 5-3-2 instead of 4-4-2 then of course, your squad needs to adapt like any team in real life. If you keep rotating your players to suit the change in formation, they're not going to be happy if they're contracted to first team football and they only play 15 a season!
As I said, there are millions of variables, you need to find a tactic, LET it work, give it a season and let your players get used to it, keep an eye on it (dont go on holiday for the season) and tweak it the best you can, then you will get the best out of it you can. Nothing comes quickly in FM, you need to be patient!