hi . Are these jacks meant to leave in place or should i shore up with wood after raising the flooring to the right height?

They are intended for temporary use. Not tied down if there's an earthquake. Also assume that any jack that can be reached by kids (or others?) is going to get cranked higher or lower. As the other review says, very slow adjustment to lift the house, then replace with the correct length of post.

I absolutely would place support under the floor and remove this jack upon completion. Any raising of the floor should be done slowly and over a course of at least a few weeks. About half a turn per week.