The Shimano UN** bottom brackets are an answer to a commuters problems. On my commute bike the BB had to be overhauled every month to keep it running in winter months, and probably should have been done every week. Same with the hubs. Snow, salt, grit carried by the snow all got into the hubs and bottom bracket. No way around it. Even with this high level of maintenance the BB had to be replaced every season after the winter commute months.
Along came the UN52 and I have yet to service it. Going on 30 years with the same Shimano UN52 bottom bracket. Works flawlessly. Every bike I have a UN** BB in, I have had zero maintenance and zero failures. Cannot claim the same for traditional cup and cone with the exception of the Campagnolo Nuovo Record bottom bracket used on my race bikes, but then again, I serviced the hubs and BB every other week!