I did use the YS-250 manually for about 3 months and am now on the Heinrichs converter. Happy with the strobes themselves, about 15 dives. Most of the research done was asking shop owners and reading Wetpixel.
Also happy with the Heinrichs, the only difference to the Sea&Sea converter being the TTL adjustment hidden behind the plexiglas cover, out of range during a dive, then again I don't play with these much. There are a few stories on Sea&Sea converters flooding, however I have no personal experience with one.
Lost flash ability on 2 dives so far, when water got into the TTL bulkhead (not inside the housing), need to change that o-ring, but that's it really.
I love the fast recycling time of the YS-250.
Cheers,
Simon