The geller stuff was a bit basic:

It seems like you have to add your own power supply?
A competitor had a 9v block battery socket on the bottom of the pcb. Which raised it a bit and made working with it nicer.
Had he made it a bit nicer with some kind of enclosure (plastic or alu or even custom alu milled) , some kind of burn-in service? , some kind of calibration "certificate" he might have been able to have something that his competitors did not have at that price point. Thus seizing a bigger market share for himself.
Also some kind of marketing might be needed to survive in such market.
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The pro over the china product would be
- "trusted" component sourcing
- EU / USA quality assurance
- faster and possible cheaper shipping
- possible better build quality and consistency
- possible better documentation
- possible burn-in service
- possible better service
- possible better "calibration" sheet / proceedings
- possible re-calibration service
So there is a lot of room how it could be improved.
But I would not base a company one one niche product , I would do multiple websites / business selling one or a few niche products.
One tip for looking for a niche is look at hobbies. Many hobbies cost 1K to a few thousand dollars.
Look at RC / FPV / UAV , to build a decent custom one you are over the 1K mark fast. Make one or more products that solve a problem for this market and you have one a reasonable market to sell to and two almost to none competitors for months to multiple years selling reasonable margin devices.
Photography , camping (solar , charging , portable battery) , E-bikes (custom motor controller? , battery management system) , aquariums (monitoring , telemetry gsm , wifi ...) , design some measurement / data-logging device for the education / scientific market, make stuff for pets (animal tracking) , some kind of automation device for some market ....
So many markets to get in to... I would just pick a few , spread the "risk" and make your workflow so that as little time as possible goes into these businesses. When you have a regular stream of orders let students / kids pack and ship the orders. This gives you more time to do useful things. Make good documentation (manual, videos?) , FAQ's so you are not spending much time answering "dumb" questions.
In the meantime you could do some contracting if there is not enough sales revenue to pay your reasonably needed salary.
For contracting clients like if your are like a one-stop shop:
- Design schematics, Design pcb's
- Assemble prototype pcb's for clients
- Do some capacity of 3d CAD for cases or whatever (you may not need to use it, but they like it that you can)
- Know something about manufacturing techniques: 3d printing, laser cutting cnc milling
- Being able to do small 3dprinting , laser cutting and cnc jobs. These machines are pretty cheap these day in age. If you can't pay for them yourself than try to find a hackerspace or fablab in the area where you can do it.
- Being able to do embedded programming in a semi-professional capability
QT / VB / C# / .NET programming for GUI's and Some C , C++ programming for embedded programming. Having a reasonable base for programming is a plus. When you have that than it is not too hard to make something in a language that you have not used before without to much start up time.
Having experience with linux is also a plus (command line, scripts , making / compiling / executing a program).
Build your portfolio , raise your hourly price when you get more experience and have more jobs in you portfolio. EU / USA companies are willing to pay reasonable wages (30 - 80$ /hr) depending on the work and skills you have. Only do jobs that will end well , are you not sure that you can do it than It would be wise not to do it.
Once a you have a few companies that like your work you will most likely have they as a long time customer providing a steady stream of work part- to full-time.
Keep your overhead low. Accounting for small companies is around 500 euro a year here and than they do all the work for you. The only thing that you have to do is send them the invoices and check their work once a quarter.
Try to do as much mechanical prototyping in house. An A4 Mylar stencil might cost you 25 euro delivered. And you might need 10-20-30 a year for proto work for customers. Why not buy that laser cutter machine for 1000-1600 euro and do them yourself. Now you have the ability to laser cut cases / windows / engraving (service) and you have the ability to make your own stencils which saves you money in the long term. It also offers more flexibility.
A low end pnp like the liteplacer is ~1000 euro.
It does a reasonable job and requires short setup time when the workflow is set up properly. Now you can offer a service for your clients by assembling board for them in the 0-20QTY range without you spending all those hours doing it by hand. Let the machine do most of the work and just check on it.
(And no you may not make it a in house pick and place discussion

)
Same for 3d printing and cnc milling.
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Focus your portfolio on the job demand. Look at which jobs clients have open (online on UpWork or whatever) and try to do some personal projects to put in your portfolio regarding those things.
Some "Hot" things:
- IOT (wifi , Bluetooth, m2m ...)
- Wearable (screen? , Bluetooth LE , battery management)
- Arduino / BBB / Pi shields
- Automation (telemetry 3G/4G , WIFI , Bluetooth ....)
- Energy Harvesting (got a job because I had it in my portfolio)
- low / med / high power rf designs (look at TI)
- Motor control (UAV market , 3 phase motor control (ESC's))
- Portable battery solutions (lots of those custom solar battery things)
- Portable GPS tracking devices
....
Now enough typing , lets see what the reactions are.