I broadly agree with laalNick, and jniel's opinion is one that I know many employers share in my experience. Like jniel says, if a person has studied alongside working, perhaps while also raising a family or doing whatever else might reasonably command their attention then I am particularly impressed. It will not be an ideal route into some professions, but that is true of many universities and courses. You do need to consider what you might want to do in the future.
I have never studied with the OU so cannot offer first hand experience of the course(s) but do know several university lecturers/professors personally who think that an OU degree (at least in non-STEM subjects) would provide a perfectly reasonable basis for postgraduate study. There have been several OU students on TSR who have progressed to "top" universities, notably Cambridge, for their postgraduate studies and I know several people personally of whom the same can be said. If nothing else, this suggests that the OU degree will equip its students with the same academic skills as most other universities.
You also need to consider how you think you learn best, and the kind of environment that will motivate you. I think most people would benefit from attending a brick university if possible, but some people (like myself) prefer to teach themselves.
Best of luck.