Will jailbreaking make my device slow forever?

I want to jailbreak my iphone 4 its a bit slow already but i wanted to know if it would slow my device forever as if i wannt to restore i want it fast again my friends have told me it will stay slow but i don't know someone tell me?

When you jailbreak, it will slow down a bit as there's quite alot of data in a jailbreak. If you want it to be faster just restore it.
I've done this before on multiple models.

I agree with Harry, my experience is also that the jailbreak will slow down the phone.

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