Due to editorial mandated tie ins, etc. Simon doesn't have too many appearances under his belt. Despite this he still managed to get some good character development.
Simon has a somewhat sci-fi version of Batmans' origin. The Amal family were traveling down a road when a spaceship crashed in front of them. His parents were killed and Simon swore vengeance against all aliens. Clouded by the need for revenge he buried himself in his work and used the familys' vast funds to make himself into a weapon to fight against his alien foes. This brought him into the Outlaws path when he targeted Princess Koriand'r. After the battle Starfire wanted Crux dead, Arsenal thought it would be overkill on an already unconscious enemy which left his fate in Red Hoods' hands. Jason (*1) decided to drop Simon off at Arkham even though doing so upset Kori.
Some of the story was retconned although I'm not sure if this was because of reader outcry or Lobdell simply forgot what he wrote. (*2) Originally Simon had alien DNA now his powers come from DNA taken from some of Batmans' rogues. Jason only gave Arkham the Crux name yet Simons' real name is the only one they seem to know when he returns. Of course Jason also told them to keep Simon constantly sedated which they either ignored or didn't know the proper dosage. Simon gets therapy and manages to get past his own anger. It's very fitting that Jasons' the one he has at his mercy and is the one he's grateful towards since it was his choice that allowed Simon to regain control over his life again.
Simon helps the Outlaws take down an alien invasion then escorts Kori and her sister back to the planet. RHATO was about people being hurt and trying to heal afterwards. While it might not have been intentional on their part they did help someone else through a hard period in their life. It'd be a shame if we didn't see more of Simon. We never did learn who was responsible for his parents deaths. According to Simon the pilot kept moving like it didn't matter that they just killed innocents.
*1 Jasons' reason, at least the one he gave Kori, didn't make much sense. He claimed that there were no laws against people killing aliens but why would that matter to a group of Outlaws? Since Jason does what he has to in order to protect those he cares about it seems odd that he'd let this danger pass. He could have felt empathy for Simon because of his backstory and not want to let Kori know that. It might have made him uncomfortable to pass judgment on someone he didn't even fight/know. There's also the fact that Simon didn't try to kill Kori when he had a chance. Simon tried to take her powers away instead.
*2 Lobdell has admitted to "winging it" to make his stories more unpredictable. Since he was writing three books at once (RHATO, TT and Superboy) he forgot where one plot in Superboy involving Lois Lane/a snitch was heading.