Mirrors are interesting. They hit very high performance metrics in a small budget. However they have this pesky issue of requiring an electrostatic field. Conduction losses are a killer, scale up in nasty ways, and ablate material quickly.
In terms of inexpensive neutron sources: they're perhaps some of the best we have.
I recall hearing a scientist from the lab say that was the way to go and they mothballed it because they wanted to focus on weapons research.