If any of the so-called SAR experts cared to look at the photos which were posted by Megan, they would have seen the ADELT fitted on the starboard side of the tail boom. Also all Bristow helicopters operating in Nigeria have some form of rescue beacon carried in the dinghy or dinghy stowage and each crew member has a beacon in her/his life jacket.
In other photos I have seen of the aircraft floating upside down in the sea, all the flotation bags appear fully inflated, so the capsize of the aircraft seems likely to be caused by other factors - maybe the sea state? I have no idea.
The wait of 2 hours mentioned in the newspaper report may, or may not be true. - Nigerian papers are notoriously unreliable. With the total absence of any credible SAR service in Nigeria, it was most likely due to it taking that long to get a ship there.
There have been several times that the offshore oil companies in Nigeria have talked of funding a dedicated SAR helicopter, the last one I know of being around 4 years ago to have fully crewed, SAR S92. All have foundered because of inter-oil company squabbling as to which was going to run it, or lack of funding. It has always amazed me that as one of the largest oil producing nations, Nigeria's NEMA has had no offshore SAR capability.
The cause of this ditching is not known yet, but as all the occupants of the aircraft have survived, the crew will doubtless be able to assist the investigation. The aircraft has been recovered, so it's likely cause will soon be known to Bristow. Hopefully the management will then release the information in the interests of safety (and to stop disgruntled employees using social media to air their grievances).