Former Redmine user here; well, I get around so I see a lot of different systems.
Back, c2005 I think, I was CTO-ing for a company that was going through some management changes. The outgoing CTO was a "build it all in-house" type (which I get!) -- however, this dude was extreme -- so in addition to building their own App to make money, they had their own Framework and ORM and X and Y an Z -- which included a bug-tracker. Naturally, it was SHIT and nobody had time to work on it -- cause well the App needed to work and Framework (and ORM and X...) all needed actual things.
One of my first steps was to drop that dead weight. One of the juniors had recently heard of Trac so we dropped that in place and migrated all the tickets (give this junior some stake). A few years later the team was not excited about Trac anymore and that same junior (now medior) was pushing for Redmine -- I was not excited to switch (I love stability).
So I made them do the migration testing, cloning, writing the guides for migration, writing the quick-starts for the team -- sort of "run the whole project". It was not trivial, there was a lot of pre-Trac legacy BS that had just been jammed in from that migration; so we wanted to clean some of that as well. Great learning experience for the team member -- managing and coding/digging in arcane/foreign systems, integrations, etc.
Blah blah right...
Well, that company now has that same junior, now senior in the Big Chair; and they still use Redmine. It's been there for like 15 years! I'm not a daily redmine user (anymore) but Redmine has a nice place for me -- less as a bug tracker and more as a give-a-junior-some-growth-opportunity.