Had experience with Sigma, the only thing good I guess was the Jargon feature.
I had experience with MY account going through the same thing that fionn did, prior to using Sigma. My skin got changed to some pink 'cute' girl shit so I reverted it and changed passwords as well. If its closed source I wouldn't use it.
edit: deobfuscating the brainfuck named sigma and there are tons of classes with unusual characters