Cassia oil certainly is still used in perfumery, but you canít use more than a trace before you start to get into difficulties with IFRA compliance, so if that is important to you, you should probably avoid it. The problem is that it contains some chemicals with suspected carcinogenic effects that are active via skin absorption: safety is a relative term - compared to smoking 40 a day itís pretty safe, compared to using a perfume without it, less so. Whether you want to use it in a perfume for your own personal use, depends on your attitude to that kind of risk.
I have a small amount of a CO2 extract of cassia and the smell is fantastic. I had in mind to use it in a reed diffuser, but have yet to find a solvent (other than supercritical CO2) that will dissolve it all.