If a user has to go through a 301 then loading will take a little longer. If a bot hits a 301 then it will delay when it gets around to crawl the real page.
Search engines will need to discover the new 301s, drop the page from the index, then later crawl the new destination, and add it to the index. Search traffic may drop for a while. If mistakes are made, maybe for a long time.
Users nor search engines care much about the structure of a URL. How your pages link to each other is far more important.