Nick VK4PP sent one of his LPFx4 test boards to Warren WA8TOD for blow-by testing. It looks like the bare PCB has excellent isolation between its input and output, of around 90db.
Matched with RF rated and separate in/out relays this board will perform very well. The updated pic above shows a few tweaks and more ground stitching.
The only downside is the US$1.50 each relays (x8). Relay K3 can potentially be reused, or you can source AXICOM relays for a bit more.
Nick is interested in feedback from constructors on the level of demand for these boards.