I bought a YS110 as a package with Sea &sea DX-1G. This combo only has a optical fiber trigger option and many people myself included experienced intermittent triggering.
I think most of that problem is too insensitive optical trigger. S&S were not very good in providing explanation an support for this. A little plastic piece that put the fibre straight in front of the flash was one solution that didn't quite solve the problem. In my case both TTL and manual actually worked fine, part from that the strobe obviously missed some flashes.
The YS110 works for some purposes, but i think in general the used price on these is too high based on the limitations.
Myself I have a working workaround, don't really need and use TTL so I have made a mini-strobe that fits the housing and that puts a very strong pulse straight into the fiber with successful trigger every time.
Cheers
/O
(I would not mind buying another used YS110 at the right price... ;-)