TL;DR: It was a great plugin, until it stopped functioning properly and trying to get ahold of the plugin dev is damn near impossible.
I've been using this plugin for almost 2 years now. It's a fantastic plugin. Does exactly what I want it to do, simple to use, coded well. I started using it I think in 1.11, and I've been using it since and upgrading with no problems, using the same files that I've been using, and when I switched to 1.15 and upgraded the plugin, that's when the problems arose.
All of the files that contained players' playtime vanished. All of the backups that the plugin automatically created also vanished. This was over 1 year of playtime for every player who joined the server, all of it gone. This was a serious problem. I only do full server backups for the world because I home host and don't have enough money for lots of storage, and it was appealing that the plugin automatically created backups, but due to this issue, I lost all of the important files completely out of the blue.
I joined their Discord server and explained my issue. The plugin Dev, Staartvin, did respond to me and said that he didn't know of the issue, and told me that the plugin does not have the ability to delete the files. I found it very odd since no other plugin suffered data loss, so it wouldn't make sense for this to have been caused by something else.
I started looking into the issue and did find another person with the same exact issue. Thread here:
https://www.spigotmc.org/threads/autorank-issues-alternatives.378972/
This affirmed that this problem wasn't a fluke caused by my server, and that this is an issue that has happened before to other people. This is a pretty large issue, and I tagged him a few times on the Discord server but got no response.
I started to restore the playtime to the best of my ability, by creating a file, where I looked at each players ranks and gave them the minimum amount of playtime for that rank (since my system was that you get a new rank w/ perks after a certain amount of playtime). It's not a perfect fix since players would still lose playtime, but it was good enough since the files are now gone.
I wanted to use the /ar import feature, but as I found out, that is also broken! This was also confirmed by another player on the Discord server that /ar import was not working. I tried it, and it would import about half of the file, but then reset the file after a restart anyway. So it was useless. The plugin was still deleting files after seemingly every restart, and the import feature isn't even working properly.
After tagging Staartvin on multiple occasions and explaining my issue, I still did not get a response. My server has been down for over 1 month and the problem is not anywhere near fixed, so now I'll have to look for a new autorank plugin and hope that it can offer at least half of the functionality that this one did.
Overall I'm very disappointed. I will say that, when I was getting responses from him, Staartvin was very nice and understanding. I do think he is a good guy, but I find it pretty annoying that I'm not getting any responses from him on the Discord server, about a bug that is basically making the plugin unusable for me. I'd be willing to remove my review if these bugs are fixed, my Discord is Cam#1499.