Sadly, I'm very disappointed with the L-858... and I haven't even had a chance to use it on a shoot.
I was thrilled when I heard that there was finally going to be a meter that could meter for both HS and HSS shooting. I especially wanted it for use with my Elinchrom ELB400 and HS Head to minimize chimping to hone in on the right exposure. (If I'm using one of my HSS strobes, it's not quite as bad since I'm using E-TTL to a degree.)
The problem is, it simply doesn't work. The Flash Duration Analysis (which tells you the flash duration, at t 0.5, the duration in milliseconds at that point and the f-stop) will NOT work when the duration of the strobe is longer than the shutter speed. For me, that means that shooting above 1/320 of a second yields an f-number of UNDER. (Sekonic (Japan) gave me this information which explained why I couldn't seem to get an f-stop reading when I was higher than 1/320.
I have figured out, to a degree a workaround that may possibly work. I meter at 1/320, get the f-stop, then crank up my shutter to, say 1/1000, while opening the aperture the same amount. So, 5 @ 1/320 is "about" 2.8 @ 1/1000. I say "about" because I may have to adjust power slightly on Elinchrom, or open or stop down slightly, depending upon ambient light.
I suppose the flash analysis might be useful if you are looking for short duration strobes for freeze something and want to measure it in that instance. But the promise of HS/HSS metering just is not really there. I could have saved myself $800+ (meter plus radios for Pocket Wizard and Elinchrom/Phottix) and stuck with my L-478. The L-858 is also significantly larger and heavier. It DOES have a spot meter, but honestly, it's been so long since I've used one, I'd probably mess myself up.
In all, it's a nicely made meter that doesn't deliver on it's promise. Really a pity. But my workshop/photo storage is littered with technology I tried and ultimately found not of use. I'll keep this. I might as, since I can swap out radios, depending on my shooting situation.