If you came here because you're concerned about all rights contracts, then you can click on 'copyright' under this post to get my opinions on the matter. Those opinions are not favourable.
If you're here for my advice on the matter that's very simple – don't sign. Simply explain to whoever sent it that although you'd be happy to have your work published by them, you're not prepared to give up all your rights. They might listen – several of us asked Yours to reconsider and they did.
The only way we can stop all magazines from taking all rights is if a lot of us refuse to sign any new all rights contracts, and if those who've already signed some contact the editors and explain they will no longer submit work under all rights terms, either in their own name or a pen name. We could achieve this together. I cannot do it alone.