For many years, I accessed the email accounts on my server only using Horde, so when it was removed, I did my best to give Roundcube a chance at winning me over. I liked some of the functionality (once I tweaked the settings), although I miss the option to have attachments stripped as items get filed in Sent. However, the current dealbreaker for me is what appears to be a greatly increased amount of computer memory being used on my Windows 10 PC by keeping a Roundcube tab active in Google Chrome. For several weeks, I experienced increased lag time when switching between active applications on my PC, and while I haven't spent the time to test my theory, I think it could be due to Roundcube. When I switched to having MS Outlook open instead of Roundcube, the phenomenon subsided. Also, when actively processing my inbox in Roundcube, I noticed frequent lags while Roundcube displayed "Loading..." in the lower right-hand corner. I know that could be due to things like the efficiency of the connection to my server or server load, but the load on my VPS is typically below 0.10.
As currently configured, I don't have any "Filters" options in my Roundcube settings, but a quick search shows that "ManageSieve" probably needs to be configured in Dovecot in order to enable Sieve filtering options in Roundcube. The option to have messages automatically filtered is pretty important, IMO.
Sorry this was a bit long, but for me, the jury is still out on Roundcube.