[Rusty]

Are you talking about the future subjunctive, or about the two forms of the imperfect subjunctive? I use the two forms of the imperfect subjunctive, but have never heard anyone use the future subjunctive. I'm aware of it only because I read old literature.

The link I posted says the future subjunctive is dead in modern Spanish.
I googled "Spanish future subjunctive." I read what the first twenty web sites had to say about it. As far as the spoken form, they described it as nearly obsolete, infrequently used, dead, all but dead and rarely used. The written form appears in legal language, classical literature, poetry and some idiomatic expressions.

You can also google "futuro de subjuntivo" and read what the web sites say. All speak of its desuso. Its demise is evidenced by a blog entitled Salvemos el Futuro de Subjuntivo.
Said one of the respondants of the blog:
"El futuro de subjuntivo por mucho que pese a algunos ya no existe en nuestro idioma, es una pérdida de tiempo intentar defender lo que en la actualidad no tiene ningún uso práctico. Y si, en este post hay veces en que aún por encima está mal utilizado, cosa que es lógica porque como ya no se usa, la gente no sabe usarlo."

Are we speaking about the same thing?