Included PSU should work just fine with the flex. Had zero issues with my 440 EP.
Only drawback about the case is it's only really any good for 1 HD/1 optical drive setups, but you could cram 2 2.5" HD's in it with a little effort.
I have a Lite-On SATA DVD-RW and SATA Patriot SSD in mine on the 440 EP, works well.