I've never gotten to play with the singulo, but the supermatter seems way less dangerous in general.
1) It takes a long time to explode if something goes wrong. Assuming the AI isn't messing with you, this makes it basically impossible to *not* eject, at which point you either order a new one or just go with solars. And even if it does go boom, it won't affect much beyond engineering and the nearby maintenance corridors. The rest of the station, and the solars, will still work fine.
2) It's output is currently low enough that you have to take some *minor* risks to get REALLY good power. This makes it more interesting for engineers: We actually have to watch it, and even when its output is good, it's not quite safe enough or high enough to make the solars useless, so we have a reason to do those as well.
3) There is no way to remotely cause it to fail (unless you are AI). As Antag, you MUST be present in engineering for a while sabotaging the supermatter, and your sabotage is either very loud or fairly slow at which point a diligent engineer can catch you or stop whatever you've set in motion.
This actually happened in one of my favorite rounds. I was coming back from doing Solars and found the captain doing an inspection and found someone else messing with the engine. They tried to claim they were 'turning it on', but a quick examination of the console showed it was quickly getting out of hand. A brief bit of combat and an explosion later, the traitor was splattered on the engineering floor, the captain was asphyxiating while the room depressurized, and I was ignoring the both of them while I ejected the engine
... oh don't give me that look, I got the captain out safe. Didn't even have to clone him.
Compared with the singulo, where...
1) On a good day, the station is fucked. On a bad day, the escape shuttle is fucked.
2) It produces enough power that you might leave it unattended, which means...
3) The antag can get in, set a remote signal to the emitter console, and then trigger it later at any point. This can make it very difficult to stop, and kind of uninteresting for the engineers. Though if they see the console trigger in front of them, they'll know what's up.
Though in both cases, the AI is just ridiculous