So even in your opinion it's in the same space and similar.
Don't work for them, don't have them send you anything remotely technical (specifications, code, documentation).
Don't work for them, don't have them send you anything remotely technical (specifications, code, documentation).
And if your project becomes big money, they may sue because they are still struggling to get by and you aren't.
So I think your impetus to turn it down is the correct one.