Functionally they're very similar and both are designed to be used with the same software, TunerStudio. If you're happy to assemble the board yourself they both look like a similar amount of work.
There is a larger, more established community for MS, and looking through the forums, someone has probably done something within spitting distance of what you want. Speeduino say they are still in development stages, but the FB group and forum are great for resolving problems and getting you going.
I chose Speeduino because it ticks a few boxes for me, and the money I saved up front can offset things like new temp sensors, an SLC Free kit, and buying the wrong damn manifold.