This solution was surprisingly easy to configure. It has a much higher bang for the buck than other products we evaluated. The replication is very fast.
The most valuable feature for us is policy based replication, which lets you add a VMware Virtual Server and NAKIVO will automatically back it up provided that it fits the policy.
An improvement would be to give us more control over the email alerts, with different emails going to different addresses based on a set of rules.
We used Xackup with XenServer prior to this.
I found that this solution was surprisingly easy to configure.
I suggest downloading a trial copy from the website and take it for a spin. It has straightforward licensing.
We also evaluated Veeam Backup & Replication.