Elphinstone is a serious dive site, not a casual snorkel stop. The reef sits offshore with steep drop-offs, current, soft coral, and the chance of oceanic whitetip or hammerhead sightings in the right season.
Go only with a reputable dive centre and listen if they require a check dive first. Conditions can be demanding, but for qualified divers it is one of the main reasons to choose the Marsa Alam and Port Ghalib coast over Egypt's busier northern resorts.