Deke Slayton addressed Gus’ door in his book, “Deke”. His opinion at the time was that Gus had likely taken off his helmet and had it sitting on his chest while he continued his post flight checklist. The Mercury capsule was very small and with his normal movements and the wave action Deke thought it likely that the helmet accidentally bumped the ejection button which triggered the door. As evidence, every other astronaut that hit that button had received a decent sized bruise on the back of his hand (not sure from what, but something from the hatch opening would hit them) but Gus did not have a bruise.
All of the astronaut biographies I’ve read speak very highly of Gus. The astronauts tend to be honest and they are not afraid to point out personal failings which gives credence to Gus being seen as a very skilled and competent astronaut and engineer.
Based on the biographies I’ve read, this is how the 7 seem to have been perceived behind closed doors.
Alan Shepard. Very skilled and competent Navy pilot which is the reason he was selected to be the first American astronaut to go up. He was somewhat bipolar in that he was either very gregarious and joking, or very icy and serious. Nobody liked the icy side. He was apparently the most unfaithful of the 7 to his wife, and that’s saying something. He was grounded because of an inner ear disease during Gemini and worked in the astronaut office with Deke Slayton. During Apollo he had surgery to fix his ear and received clearance to fly. He’s the only one of the original Mercury 7 to actually walk on the moon.
Gus Grissom. Well liked but very quiet and serious. Was considered an exceptional engineer. As I mentioned above, nobody thought he panicked under pressure.
John Glenn. He’s the only one that acted in public the way he acted in private. He was somewhat of an overgrown boy scout but not really a prude. He had high ambitions and used his astronaut fame to propel himself into public office. In the movie “The Right Stuff” there’s a scene where he confronts Shepard about his philandering. On the surface it looks like it’s a question about morality, but the real truth of the matter is that Glenn and some of NASA’s brass had found out that a reporter was going to go live with a story about Shepard’s affairs. They knew that if that were to be published the scandal would destroy the program so they managed to convince the reporter not to publish but Glenn was furious that Shepard was unrepentant about the mistake and unwilling to keep things discreet.
Deke Slayton. Deke was supposed to go up 4th, but during his training NASA doctors discovered a minor heart defect and grounded him. Deke went on to become the head of the astronaut office and was the one who made all the crew assignments. All of the astronauts and administrators speak very highly of him. Eventually Deke was allowed to fly on Apollo Soyuz.
Scott Carpenter. Scott was very adventurous and a gifted athlete. JFK said in private that Scott’s wife was the prettiest of the 7. But Scott was a dreamer, and not a very good astronaut. He failed to listen to Mission Control on his flight, expended a ridiculous amount of fuel on wasteful maneuvers, and nearly burned up on reentry. Mission Control banned him before he was on the carrier to come home.
Wally Schirra. Efficient to a fault. He wanted a space mission to have very clear goals, and he wanted all of the tasks assigned to the astronauts to be for the purpose of completing those goals. Of those tasks, Wally was excellent and precise. In Mercury and Gemini Wally was able to get the types of missions he wanted and he excelled at them. After Gus died in Apollo 1, Wally was given the honor of taking the first Apollo flight. But Wally was cantankerous, he refused to do many of the “fluff” tasks such as video recording and interviews. And he argued with Mission Control and refused some of their orders. Not only was he banned but his entire crew was banned by extension. I always felt bad for them, any other commander and they would have probably had a better career.
Gordo Cooper. He was a hot shot and unpredictable but an extremely capable pilot. He very nearly didn’t get to go up in Mercury because he made a fly by of an airport so low that the guy in the control tower was actually looking down at Gordo. NASA brass wanted Shepard to fly his mission, but by that time Deke was already in charge. Deke didn’t want to kill Gordo’s career so he kept him on the mission. During the flight, Gordo had serious problems with his spacecraft and expertly brought it back to Earth. He flew again in Gemini but had so many arguments with NASA that he was never assigned to another mission. He quietly left NASA when he realized he wasn’t going to fly again.