The Mongoose can only do powertrain programming. Standard J2534 can only touch EPA mandated emissions-related modules (ECU/TCU). Due to this being a J2534-2 (version 2) device, this can go beyond ECU/TCU to program/flash ABS, TPMS, Airbag, SRS, SAS, and other modules depending on the OEM software. With Toyota and Honda, for example, you can do all of those things with Techstream and i-HDS, respectively.
If you ever need to replace one of those modules or modify values within them and reset, reprogram, or do a "learning" procedure before it will work (in accordance with OEM service info), this is one of the only tools that can do that, other than OEM/Dealer GDS device.
In addition to that, the Mongoose is great for what it does but is not available for all makes. There is no Mongoose for Hyundai, Kia, Mazda, Mercedes-Benz, Mitsubishi, or Subaru. Not super popular makes, but there are definitely people who want to program, tune, and replace modules on them. You need the right tool to do so.