...that looks interesting; similar concept. In fact there's been some debate about whether it was A Little Thunder that shut down Submarine's US distribution for patent infringement...https://www.submarinepickup.com/usa
Both have their pros and cons. Eg Submarine Pro lets you choose any combination of strings, while Thunder offers a low-note-priority option. Submarine simply clips on while Thunder is a a pickup replacement. Thunder has the octave processing built in, while Submarine would let you use any effect on its outputs.
(There's a demo of someone jamming on an acoustic with Submarine bass here
. With the Submarine the quality is going to depend on what effect you run it through...but I think the acoustic Thunder
demo posted above is pretty hard to beat...)