So £1000 for a 0.25% investment, paying dividends only on profits, possibly requiring the shareholder to contribute marketing etc. effort too, in a company that's yet to turn any profit (no debt is easy, especially with a huge cash injection first, but profit is hard - and no debt "aside from the initial investment" sounds like you are demanding it back and would be first to be repaid, so that means how many units sold until the company is in any profit at all), has taken thousands already from pre-orderers and (mostly) not yet met their preorder obligations yet, has all its money tied up in stock and manufacturing contracts with foreign companies that have been quite unreliable and where replacements are actively being sought, has shipped 900 units in two years (that's just over one unit a day), is obliged to push out several hundred/thousand more units (not counting RMA's) before taking any more orders, where the shareholders would have virtually no say and several complex tax/exchange/contract issues, where vital parts of the stock are owned by a foreign and quite unaccountable third-party company and yet there's nothing on paper about that, where the main shareholders of the company actually rely on other projects / companies / business income to provide them with a living (and thus have nothing more to lose if everything goes titsup), where there don't seem to be any real "employees" of the company in question (merely those involved in the other ventures of the people involved).
For OP, it sounds reasonable, but for an investor, in the space of one single forum post? It already sounds a bit dodgy. If it was Dragon's Den, I think we'd be hearing "I'm out!" rather quickly. I daresay there's money that could be made if you were brave (and lucky) enough but this sounds a pretty long stretch to get a reasonable deal for all concerned. It sounds like a request for a bankroll of a huge magnitude to me - a whole quarter of the company just gone for cash with virtually zero other benefits by the looks of it.
"Gimme £1000 and I can get you 100th's of a small percentage of some yet-to-be-seen profit made after we've potentially paid off ALL our initial investments, customers and suppliers in a company that's little more than a shell, has multiple unwritten contracts with closely-related companies that hold the top talent we use, but has managed to spend many 100's of times that investment already, at some undefined point in the future... possibly, after tax and currency conversion and legal costs."
Bargain.
(It'll be interesting to see how this post gets censored, by the way).