Detecting common problems right away. Many profilers leave you on your own with their data - interpreting it is up to you. In contrast, JXRay searches for many known memory problems upfront. You get a report with your heap dump analyzed for memory leaks and more than ten other common data inefficiencies (data duplication, suboptimal use of data structures, etc.). Any anomalies are highlighted, and you see them right away.
Knowledge of internals. JXRay has knowledge of implementation details of most of the common Java and Scala collections: maps (e.g. java.util.HashMap), lists (e.g. java.util.ArrayList) etc. That allows it to accurately calculate how much memory your data (workload) take and how much is the implementation of collections themselves. In certain cases, e.g. when you allocate a large number of ArrayLists with just 1-2 elements in each, their overhead can be surprisingly high!
No-frills tool. While it may seem counterintuitive, the fact that JXRay has no GUI and produces a simple text report, has clear advantages. You can easily run the tool on any machine, including the one where the heap dump was produced (that often has a lot of memory, is on the cloud, behind a firewall, etc. - very unlike your laptop). And once the report is generated, you can look at it anywhere at any time, send it by e-mail, publish on wiki, etc. The information is easily searchable and its intuitive presentation makes it easy to understand by anyone.