Something like a NanoVNA is complex and can't be easily cloned without having to iterate several cycles in performance tuning & verification. There is a good chance people trying to make cheap clones won't want to put this effort in, they just want to get to market with as low of costs as possible and ride the existing product name. They will also probably greymarket source the parts, so performance will vary between batches. You can potentially use this as your advantage.
When your item gets cloned: buy each clone, analyse its performance and list its shortcomings on your sales website. Make it clear that yours (bought directly from you) is still better and worth the cost. Of course base this off actual tests, not just guessing based on visual difference, you are a biased party after all.
(I'd even go as far as publishing a document saying "If you are going to clone this device: these are the things you are going to stuff up, please read carefully" so you can laugh at them afterwards
![Cheesy :D](https://www.eevblog.com/forum/Smileys/default/cheesy.gif)
)
EDIT: Whilst I'm here: if at all possible try to avoid getting into debt to make this. If your product gets cloned and you're worried you won't make back costs then that's one problem, but in reality there are many more factors that could prevent you from making your costs back. Performance, reliability, competition, small market, economic woes, parts shortages (this is slamming lots of small device makers!), etc. Example comprimise: If you don't trust overseas PCB fab & assembly services (I suspect most sell & share your designs) then maybe make the device out of two mated PCBs from different suppliers, rather than buying PnP + production equipment yourself. Maybe consider that later if your business becomes reliably successful.