Getting an external USB HDD would be more cost-effective if your current USB memory stick is too small for you or upgrade the internal HDD of your PS3... (either way it's pretty pointless too spend extra money on an old PS3 now... unless you actually still play a lot on it...)
As for your question whether CFW PS3 Multiman can read burned PS3 blu-ray discs, that you have burned using a blu-ray writer on blu-ray writable discs: Yes. It's just not worth the money unless you already have the needed stuff in house as pointed above ~~;;...