Apart from the fact that things could go south between you and the client, if I was a client and you agree to a contract outside the platform, I should be worried. It doesn’t portray you, the freelancer, well. This is what I mean, I would run from a freelancer if they suggested that we take the work outside upwork, it means they are doing something shady right up to something shady and if they’re willing to do this, they’re willing to do other things. I might be wrong but that just my own perspective. It makes absolutely no point to take work off Upwork because you want to skip the platform fee. If the platform wasn’t there, how would you get your client in the first place? Upwork saves freelancers tons and tons of time and aligns them with opportunities that would have never ever happened had you searched on your own.
It’s a red flag for clients, and some clients can even go as far as reporting your account.