I have not been. When researching a trip to another destination, I collected a listing of trip reports on Cocos. Just in case any may have content that could help, and since you posted over 20 hours ago and no answers yet, I'll share my list.
-----1.)
Cocos Diving Trip Report, 17 – 27 September, 2018 – by Dan. 11 Trip aboard M/V Argo.
-----2.)
Cocos, March 27 – April 5, 2017 – by scubadada. Aboard the Okeanos II.
-----3.)
Cocos trip report with pictures, August 2019 – by Erwin Poliakoff. Aboard the Argo.
-----4.)
Cocos on Argos, last minute trip.. – by alam555. June 2019 thread; useful for info. by divers about Cocos; rongoodman wrote some dives are deeper and can edge into deco., the bottom is mostly fractured volcanic rock and sea urchins are thick at some sites. Some dives had negative entries. Peeweediver noted you spend lots of time hunkered in the rocks; despite care he took 4 urchin hits.
-----5.)
Trip report Cocos Island on Underseahunter’s M/V Argo, 2-12 Nov. – 2016 thread by rs86.
-----6.)
Cocos Island trip with Undersea Hunter Group – Oct. 2016 report by peeweediver.
-----7.)
Cocos Island trip review with Aggressor Okeanos, Sept. 6 – 16th, 2015 – by Roger_Scuba.
-----8.)
Cocos trip report on Undersea Hunter – Dec. 2019 trip report by KrisR.
-----9.) At the risk of fear-mongering, 2017 and 2018 saw ‘issues’ with tiger sharks – one killed a woman and injured a guide Nov. 30, 2017 –
Death in Cocos from shark attack – and on April 28, 2018 one possibly ‘test bit’ the BCD of a diver at the surface –
German diver attacked by shark – Isla del Coco, Costa Rica – and Undersea Hunter live-aboard noted procedural changes due to risk concerns. Tiger sharks are a ‘feature’ of Cocos diving, but be aware.