It's open source and free. They have a paid version, but we never looked into that because we never needed the features of the paid version.

If you have a small amount of traffic or you are a small company, Graylog is just fantastic because it's open source, and it's free. You can run a Graylog instance on pretty modest hardware, but when it comes to large volumes, as we have, it becomes too expensive. 

There is an open source version and an enterprise version. The authentication is bad in the open source version, but I believe they have improved that in the enterprise version. 

I wouldn't recommend the enterprise version, but as an open source solution, it is solid and works really well.

We are using the free version of the product. However, the paid version is expensive.

Graylog is a free open-source solution. The free version has a capacity limitation of 2 GB daily, if you want to go above this you have to purchase a license.

We use the free version.

I am not fully aware of their licensing model. I should take a look at the details, as I am using a community edition. I have not looked at the enterprise offering from Graylog.

You get a lot out-of-the-box with the non-enterprise version, so give it a try first.

I use the free version of Graylog.

I cannot answer this question. Having paid official support is wise for projects.

It's an open-source solution that can be used free of charge.

If you want something that works and do not have the money for Splunk or QRadar, take Graylog.

None, as we are not using an enterprise solution.

We're using the Community edition.