I have used this method (although I skipped the sink and just let it cool in air). It will work *most* of the time, as long as you try to pitch as soon as its cooled. The thing about the cubes is you can get rid of most of the air and use hot wort to steralise the lid. Can't really do that with the fermenter due to airlock holes. Using the fermenter, you should make sure its all steralised first. My preference is to transfer the wort from the kettle via the hole for the airlock to minimise the chance air any airborne nasties getting anywhere near the fermenter (I do this with cooled wort as well)