I've shot both and actually the Inon z240 as well, not all with the E520 though.
My take on the UFL-2 is that it's pretty well matched up in terms of TTL and other software capabilities with the PTE05/E520, E620 etc. The TTL was pretty much spot on. It has a very small display, but you are able to control the strobes from the camera in RC mode, which is pretty cool. At least it has a display to show you what mode it is in, even if you can barely read it (ok, I'm 55 and nearsighted).
It's very light underwater, really almost floaty, so with the PTE05 it's very comfortable with two strobes. One thing is that you must buy the diffuser as an extra part. The Inon's and YS110a are negative.
That all being said, it's not as powerful as the YS110a, nor as wide a beam angle. It does not have as fast a recycle time, IMHO. Definitely a lot slower than my z240s, and when shooting wider shots I did have to wait for the UFL-2 to recharge.
So there's trade offs. Both are priced about the same, a tad over $600 street-price. Both are actually made by Sea & Sea. Do you want a nice, software-controlled system, or do you want a more powerful strobe that you have to adjust individually and whose D-TTL while good, probably isn't as good as the Olympus strobes.
As for Inon, they are very good units, but the support is pretty thin now in the US. I like mine, but I'd probably buy the S&S if I had to do it again.
Anyway there's my thoughts. BTW there are a bunch of the older YS110 flaoting around in stores (orange label). It's a good strobe, but the UFL-2 has probably the same recycle rate as it. Not nearly as good TTL or recycle time as the 110a. But it might work fine for you; Brian has one of each and says they work fine.
Jack
