I have been using this solution for a year or so.

I've been working with ADAudit for more than five years. 

I have been using ManageEngine ADAudit Plus for three years. We use the latest version.

I have been using ManageEngine ADAudit Plus for eight years.

We have been using the solution for approximately three years and are currently using one of the latest versions.

We have been using this solution for more than ten years and we are using the most recent version. It is deployed on-premises.

I have been using the solution for three years. 

I've been using ADAudit Plus for about three months.

We have been using the product for the last six years.  

I have been using this solution for approximately six years.