troporobo

I have also been to both and would concur that Palau has much greater diversity underwater.

Above water though, I enjoyed Yap a lot more than Palau.  It is very pretty, has some great culture, wonderful warm people, and a terrific laid back island atmosphere.  Not that these aspects of Palau are negative or anything, but the place is a bit more cosmopolitan and a heck of a lot busier

Another vote for Inon from me.  I used a pair of S2000 when I had the same Olympus set up and was very happy with the results

Avoid the Olympus stobes in any case. I could not make the UFL2 work the way it is supposed to in rc mode and had no joy in getting them to sync in manual mode

Obviously its a lot better if you can sort it out without needing to go in person of course.  But for what it's worth, if you have a long-ish layover, its possible to clear immigration and get to Beach Rd and back in an hour by train or taxi.  

The OMD comes with a clip on flash that fires the strobes using optical sync cords. I'm using Inon S2000 strobes via TTL and am very happy with the results

Did anyone have the same experience in european/south east asian airports? 

I fly around Asia (anywhere from India to China to Singapore to the Philippines to Australia) at least once a month, and to the US and Europe once or twice a year, usuallly on trips involving multiple sectors, taking over 100 flights a year.  In the past ten years I have never been asked for a credit card at check in, whether travelling business or economy, whether booked through an agent or on line, whether on an airline with top tier membership status or a first timer on a new route, whether carrying a briefcase or a ratty backpack.  Colleagues and friends have completely different experiences on the same routes and airlines, and none of us can identify reliable theories as to why. I have come to the conclusion that airline policies are simply not to be understood by mortals nor predicted through any kind of logic.  I realize that is of no help at all . . .