Hi Tim, (I’d recommend you assign a category to this thread so it doesn’t fall off the “Latest Posts”)
I’ve been looking at the DX900 as well, but as a future replacement for our DST800 on our support vessel.
This probably won’t be comparable to a DVL for positioning. I’d recommend the WaterLinked system for positioning. Speed through water for a tethered ROV? I’d say it would be a “nice to have”. The depth (altitude in this case) would be useful, but I’ve heard rumors there is something in the works. Now, if we start talking untethered autonomous, that’s where things get interesting.
I also know the @nidorobotics guys were working with the 800 series awhile back for a client so they might be able to shed some light on this.