I finally got my hands on a DSMJ system to test/review.
Looks to be a lot more resilient than DSM2 under adverse conditions -- which is good.
It's a shame that Horizon don't offer an upgrade from DSM2 to DSMJ -- it would help bring them into line with all the other systems that offer FHSS rather than "pick and stick" DSSS.
The DSMJ system is short on features but delivers on resilience.
I was quietly impressed -- it's better than I thought it would be.