Regarding no entry criteria, the OU was founded to provide anyone with the opportunity to study, including those who might for whatever reason have missed out on gaining any formal qualifications. So it's not an indication of low standards, it's a founding principle. Individual modules, once you get past level 1, very often do have prerequisites, usually a level 1 module or something equivalent.
I started an open degree in the arts in the 90s, and started an MA in social science in 2004. I didn't complete either of them but in both the quality of the materials and support was very good. I started a BSc in statistics and computing in 2011 which I completed last year, again the materials were excellent. As a comparison, I completed a maths degree at a redbrick uni in the early 2000s and the OU degree compares favourably.
I won't lie, it's hard work. I was quite happy working on my own but that's how I work best anyway and I think maths/computing are not subjects where you often need the input of others, though the course forums are there if you do. I really enjoyed it, but there were times it was hard to stay focused and I did end up taking 6 years instead of the intended 4, due to the degree getting significantly harder at level 3, coupled with parenting and work commitments. But OU degrees are highly regarded, not just for the standard of their content, but for what it says about you, that you can motivate yourself to do something difficult, for several years, while juggling other commitments. I would say it's absolutely worth it. I haven't yet looked for jobs really as I made a commitment to my partner's business for a period, but I feel it was worth doing the OU degree for what I learned about myself, and for my confidence.