Weak erection

I read in many places that PE or traction on penis may work but it can be harmful ans make weak erections

So I ask if it worth it to gain 2 cm but to be with weak erection after 1 year of hanging

May I ask where did you read that?

PE improves erect hardness if done right! If you overtrain, then expect some EQ drops.

You’ll not have weak erections for one year because you worn an extender, the effect can last maybe a couple of weeks since when you stop using it. Beside that, jelqinq at least every other day will help both gains and EQ.