If you have the chance to go and can handle the diving conditions, GO FOR IT !
As has been stated there are 2 dive shops on Okinawa that will cater to English speaking divers. Fathoms and Reef Encounters. Both charge slightly different rates, both will give you significantly different experiences in Yonaguni. Both shops offer all inclusive packages of air travel from Okinawa to Yonaguni, lodging accomodations, all meals and all diving. All travel to and from Yonaguni must go through Okinawa, so it's not a scam to get someone to Okinawa. Fathoms does a combo trip to Yonaguni and Ishigaki, but it has a different price and is at a different time of the year.
Both shops use the same dive operator on Yonaguni, from there the differences become dramatic. Even using the same dive operator, customers from one shop are treated completely different than from the other. No matter which one you go with, you don't know what you've missed until it's all over and done with and you've already spent your money.
Yes hammerheads are running through the area already and we have seen them as late as April. The underwater structures are incredible, but depending on which shop you go with, it will determine how many of the structures you see. Either way you will come away with your own thoughts once you have seen it.
The currents in Yonaguni are very strong and the water can be very rough. All dives are ended with a drifting mid-water (blue water) ascent with safety stop (no anchor lines or reefs for reference). Buoyancy control is of absolute utmost importance for all ascents and also for descents, since viewing of hammerheads is in an area where if you miss the mark even slightly, the bottom is over 350 feet deep.
This is an incredible opportunity for all to see, however if your dive skills are not sharp or you are an "occasional diver", reconsider your dive destination until you have had a chance to gain more experience. Yonaguni isn't going any place, and more is being discovered every day there. So go when your ready.
