OTOH, the concept proposed by OP is already implemented and has been working reliably for billions of years with trillions of successful deployments, while this newfangled technology you are proposing still has to be demonstrated to work...

You’re not looking at the entire cost. What are the end of life procedures when fuel is exhausted?

That's another plus! If you ever get to the end of the fusion reactor's life (which is not very likely), it's literally end of life for you (and everyone else who might still be around) too, so no need to worry about exhausted fuel anymore...

I can say the same thing about my basement fission reactor.

YBGIBG, but not in a dickish way.

Unfortunately the original developers left long ago taking the source with them, and none of them are reachable to provide an explanation even through exotic means of communication.

Trillions of deployments that are all subject to the inverse square law at a distance of 100 million miles. It's hard to comprehend how bad that efficiency is.