Feature MP Studio Lite MPViewer
Register Management Groups 1 Group n.a.
Multiple views of Management Pack files or installed Management Packs X you need to select a MP to view
Graphical view of MP references X  
View Content – rules, monitors, modules, views, tasks X No Modules (use Module Explorer)
View all overrides applied to an MP X No Overrides (use Override Explorer)
View by MP or View by Target X n.a.
Export to XML X X

So why should you use MPViewer if you have all the features and more in Silect MP Studio Lite? You can easily install and use the MPViewer, it’s only one executable ;-) For some of the missing features you can use other tools (like the Module Explorer and Override Explorer). One thing I’m really missing is the ability (from both) to export the MP to Excel. Export to Excel is available in latest version.

This should not be that difficult I would think if you use some PowerShell commands. Here an example to export the monitors for the Windows Server 2003 ManagementPack.

PS Monitoring:\OpsMgrRMS
>get-ManagementPack | where {$_.Name -like "*Microsoft.Windows.Server.2003*" } | get-Monitor |sort-object LastModified -descending | select-object name, displayname, timeadded, lastmodified
| export-Csv -Path "D:\temp\exportmp.csv"
PS Monitoring:\OpsMgrRMS