I chrono'd some DPX thru my Kahr P-9. Didn't notice any sparks. I don't recall the recoil being either significantly mild or harsh, either.
As for its "mildness" -- Altho it is labeled "+P", according to my notes out of 9 types of ammo I chrono'd in my Kahr P-9, the DPX was the sixth fastest. Its velocity was surpassed by a couple or three non-+P factory loads, including CCI Blazer 115gr and Speer Lawman 115 gr practice ammo. Theres another thread around here where we discussed the fact that the +P rating does not correspond tightly to velocity.
I believe DPX's claim to fame is not its velocity, but its ability to reliably expand AFTER penetrating various barriers. I haven't checked this out myself, but if you go search around in Marshall's website (Stoppingpower.net, I think), or especially John Farnam's "Quips" at defense-training.com, you find some examples of Corbon DPX going thru cloth, glass, and other materials and still expanding reliably in gelatin - - and maybe even more important, it seems to not deviate from its original path all that much. I have read that typical handgun bullets will deflect quite a bit when fired thru windshield glass, for example, but that DPX will pretty much stay on track.
Out of my Kahr P-9, I got the following velocities:
DPX 115 +P- 1076
CCI Blazer 115 - 1091
Speer Lawman 115 - 1127
Speer GDHP 115 (NOT the +P version) - 1174
Out of my Hi Power
DPX 115 +P - 1149
CCI Blazer 115 - 1174
Speer Lawman 115 - 1255
Speer GDHP 115 (NOT the +P version) - 1299