Here's my update on the ELB 500: Fantastic!
I have use the strobe on a number of location shoots and even for some quick still-life. I have used it both in TTL mode and manual and it has worked almost flawlessly. I have used it extensively with the 70cm Rotolux softbox (which can be used with an included modifier like a beauty dish), the 100cm Rotolux and the 5" reflector. All have been great with lots of power to spare.
Now for better detail of how I use it. When I am on location, I use it frequently in place of a reflector (ScrimJim, flexifill, etc.) because models have a much easier time with the strobe than a reflector in bright light. I use the strobe as a "micro pop" fill to keep things looking natural or to add light if I have to shoot in overcast. For me, because I shoot quickly, often with models walking, the strobe will generally keep up. (The fastest I could ever shoot using strobe is still an Einstein on 20w/s running off a Vagabond, but my Pocket Wizard sync was usually limited to about 1/320 to 1/400 on my 1Dx and 1/250 on my 5Ds.)
One of my favorite features is that I can shoot the strobe on TTL and it will give me a readout of, say, 2.9. (I have no idea what that's in relationship to -- PITA -- but it's a European power standard). I can switch to manual and maintains that power setting, so in effect "metering for me". Now, let's say I have the Skyport set to -3 on TTL and the power is still too much? I can switch to manual and dial down even more. The TTL has gotten me in the ballpark, but now I can tune to taste. I bought a Sekonic L-858D-U. Nice meter in some respects. (I can switch radio modules and so use my Pocket Wizards or switch to the Elinchrom transmitter.) I bought the bloody expensive meter because it was supposed to be able to read the HSS and HS strobes for my ELB 500 and ELB 400. Unless you are blasting power, doesn't work. So it's the old eyeball and chimping. But I digress.
Overall, an excellent strobe. I wish that an extensiuon cable was available so I could get a 2nd head and make it worthwhile. I also wish my Elincrhom ringlight worked with it, but it only works with the ELB 400. It's pricey, but if you do a lot of location work, it's well worth the money. On an average week long catalog shoot, I'll shoot between 500-700GB with my 5Ds and 1Dx. This is about 85 different shots, 90-350 frames per shot. I'd say I use the ELB 500 for about 60-70% of the shots. (Sometime more.) Until recently, I only had one battery since the battery was on backorder. The strobe would go all morning with a quick charge at lunch and then the afternoon.