[hpsdr] Current Hardware Platform ?

[Joe D.]

Forgive me if this is off-topic, but can someone point me to
hardware/kits or references to such the group would recommend for
someone just beginning to experiment with SDR.

Would like this to be the basis for an (eventual) high performance
receiver.  A look at the TAPR kits suggests that the page is outdated,
and the hpsdr webpages still talk about Mercury, but even the iquadlabs
links for Mercury do not point an available Mercury kit, but an HF1 board.

What is recommended for just entering the fray? Extensible, high
performance platform, easy to start on (others have been there before).
Joe
AG6QO at AG6QO.#NCA.CA.USA.NOAM