RX100 and external flash?

I do have some experience in using flashes. I need them to be powerful. I always bounce them in a white surface. So guide number of 40 or higher. Seagull SYK-5 sounds like the solution. If it can ignore the pre flash and be connected via pc sync I can put tape over the sensors on my old flashes.

It concerns me though that the pre flash can not be disabled. It almost pi??es me off. It must be a simple software thing to fix? Perhaps I shall chose another camera - to teach Sony. Or shall I let Seagull SYK-5 come to the rescue?
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Amateur photographer from Stockholm, Scandinavia, Europe.