Having said that, even as a hobbyist, I don't see what's wrong with it? Maybe I have written some code that is already running on my Arduino, and I want to add a sensor that is only available for RPi, without having to hop onto another platform... nothing wrong with that.
It's an i.mx8 SoC running a shitty linux distro put together by Arduino LLC. The additional MCU is an STM32. This thing is expensive as fuck while being slower than a pi and forcing you to go through the SoC to get any access to the MCU at all.
Arduino don't seem to know what they're doing anymore. They flirted with proprietary altera FPGAs that required quartus when icestorm for the ICE40 has already been a thing for a long time. Now they're trying to go after raspi industrial sales with a slower, shittier i.mx8 chip on a board that's also closed-source. Honestly, the only reason I think they were able to pull off using an i.mx8 is because of the large number of hobbyist designs with that chip they can lean on.
When I’m throwing stuff together, I want stuff to “just work”. Merging ecosystems in this way is an asset, even if only occasionally useful or in edge cases. This is the sort of thing that prevents blockers and slow-downs by increasing available options on your platform.
...use a piece of wire ? None of the interfaces are fast enough to need a breakout board.
It's not "all arduino to rPi hats" adapters either (which would be far more useful tbh), it's "that special expensive ARM stick from arduino to rPi hats".