In my opinion, Antenna tuning can be done using a spectrum analyzer with noise generator or tracking generator and it is top priority for most HAM and SDR users. VNA is a desired equipment but not top priority. So, they will first buy a nice spectrum analyzer, then more HAM equipment, and lastly a VNA. You need to show them they NEED one so it makes it top priority.
Your project is open source and if you make it attractive for the the user community to hack and improve it, you will have a differentiation. But you need to be prepared for the clones from China if you are successful.
You can take a look at HACKRF (Great Scott Gadgets) and how they promote the item online. There are lots of clones now selling on eBay as it is also open source.