IMO, these OC scuba depth records are generally a fool's quest. If you really need to do something 400 meters under the ocean, the technology to do it with relative safety exists. Get a diving bell and saturation rig and do the job right! Why attempt to do it with a minimum of equipment that is inadequate to handle even the most minor deviations from a dive plan that has a good chance of being unrealistic to begin with? It's not like this is even close to setting an actual diving depth record. It's just going deeper than anybody else has gone with equipment that is not designed to go deep.
I could understand this kind of record attempt if there was some physical conditioning the diver was doing to make them better adapted to handle the conditions of the dive, but I don't think that is what's going on here. He want's to achieve 400 meters. If that is the goal, he should have done at least 370 meters in training before attempting 400. Obviously, this has not happened, or he would be the current record holder already. It appears as though this guy is just planning a very deep dive using the wrong equipment to do a very deep dive, and doing it without putting in the effort to actually figure out how to actually plan the dive or achieve the stated goal. The odds look to be stacked against him. :O
That said, I'm not going to stop someone from doing what they want, so long as it isn't infringing on someone else's freedom. So, good luck Wael! You're gonna need it....