Note that the Blue ROV2 is NOT rated for use beyond 100 m. Its rated depth is 100 m, and the rated depth of the aluminum enclosures is 400 m, but swapping in the aluminum enclosures will not increase the depth rating of the BlueROV2. It has not been bested as a complete system with aluminum enclosures for an official depth rating, and there are other components that limit the depth, namely the foam and some cable penentrations.
The deepest we have taken a BlueROV2 ourselves was just about 320 m with @nperry and his sled, as seen here. This did lead to some leaks however.
I have also heavily modified a BlueROV2 for use by Valley Christian High School/The Quest Institute at 890 m on MBARI’s MARS stationary node platform. Among other modifications, this ROV has thicker aluminum enclosures, syntactic buoyancy foam, and Seacon connectors rather than penetrators. You can see more about it here.
We actually don’t have an official depth rating for our thrusters, as we haven’t found a limit yet. Due to our unique fully flooded design where water freely moves throughout the thruster internals, pressure isn’t much of a concern. There are no air cavities to compress, or seals of any kind. Our thrusters will definitely function well down to at least 500m or so.