x15tn is less corrosion resistant but according to BM offers higher edge retention. H1 is more corrosion resistent, and again according to BM has less edge retention. That is why the h20 fixed blade was switched from originally being H1 to x15tn.
If I'm remembering correctly Spyderco has said that their testing showed the edge retention between the two was very comparable and that H1 was significantly more corrosion resistant. But you may need to do more searching if you want to know if thats accurate or not, its been a while.
I don't think x15tn is work hardening either, so it seems logical that x15tn was just easier for BM to work with and suited their needs well enough.
My SE H1 Tasman Salt has very good edge retention, better than the 12cr13mov on my tenacious, and about where my Emerson A100 is (154cm, but softer than most people run it 54ish hrc I think)
I think Spyderco posted results on their SE H1 blades testing out at mid to high 60s on the edge.