Great comparison of the RSM 250 filtration systems. There is a small progress visible on the new one. Especially the medium rack or improved external circuit for cooling. But I still don't believe, that the stock skimmer will be sufficient to get enough nutrients from water in case of higher fish loads and SPS corals in the tank. It looks almost same like the old one. There is also visible from the picture, that the skimmer will not sit on the bottom of filtration, so I would be a bit afraid of vibrations etc.
Does anyone know, why Red Sea did not implement the system of external sump into RSM 250? I think the system on S400, S500, S650 is much better.