It doesn't matter that there was no written contract. A contract is an agreement, not a piece of paper. Just because it is crowd funding doesn't mean that you have no rights. Without reading in to all the ins-and-outs, my first instinct is that you may well be protected by consumer law such as the Consumer Rights Act 2015 if you have paid money over the internet for a good that you have not received.
It is possible that you may be able to formally cancel your "investment" (probably actually a payment) and gain a simple legal right to a refund. Even if there's an argument that you also paid for the development of the device, that's probably a service that needs to be performed in a reasonable time, and with reasonable care and skill.
Legal action for something like this doesn't need to be expensive. The first step of a claim is correspondence to try to settle (letter before action) and so can often be done on your own without paying any court fees. The threat of legal action is often enough to focus minds.
If you do need to go to court, the Small Claims Track of the County Court system may be likely suitable if JohnW still has an address / presence in England or Wales. Exposure to costs is significantly reduced on this track. If you are happy to do a bit of your own research you could look at using the Court's MCOL (Money Claims Online) service yourself perhaps with the support of a lawyer (check your home insruance to see if you have legal expenses insurance) or someone like Which? Legal Services.
If John W does not have any presence in England or Wales you could investigate equivalent processes in Czechia. (Can't link as I am a new user here after many years on the Wam, but Google "European Consumer Centre Czechia")
For what it's worth I hope mods don't mind me posting even though I am not an investor as I think this may be useful info. I am not advocating legal action - that's a personal decision - nor am I advising you (must be very clear about that). Just providing context. You will have to decide whether it's worth it. If JohnW has the money to provide the goods then perhaps threat of legal action would focus the mind/timetable; if he doesn't then you are right he's unlikely to be able to pay you back either way.
I doubt anyone would need a solicitor. But I will add the following disclaimer that I am not qualified to give legal advice and this post does not constitute legal advice in anyway and must not construed to do so. You must do your own research and decision is entirely your own.
The following is posted only for informational purposes, and is in fact public information:
'How to use the European Order for Payment Procedure or European Small Claims Procedure'.
https://www.gov.uk/government/publications/make-a-cross-border-claim-in-the-eu-ex725
The procedure for making a claim is detailed in the following and is I believe still applicable because we (UK) are still in the EU due to transition period. And I also believe the procedure can be conducted from the UK under UK jurisdiction for the reasons stated above and by the following example.
HM Courts & Tribunals Service
Document: EX725
Making a cross border claim in the EU
'Normally the usual place of residence of the defendant is the country with jurisdiction to
process the case'.
'However, there are exceptions to this so some claims can be brought in another Member State other than where the defendant resides. These exceptions mainly occur in matters
relating to:
• a contractual obligation'
'For example -
The French vendor of a motorbike can be sued in England if that is where the motorbike was due to be delivered'.
The fees are detailed in the following document are not particularly expensive and on the assumption that the plaintiff wins, all fees and interest would be payable be the defendant.
Civil and Family Court Fees
From March 2019
HM Courts & Tribunals Service
Document: EX50