As Tom says the Blix baths are fine, with one proviso that you stick to the manufacturers staed capacity. I'd also go further and say I only use two reputable manufacturers Photocolor & Tetenal, their Blix's are extremely good but other's not so reliable. (The Photocolor/Paterson line went when Champion moved production from UK to Spain).

No there's no difference between the good 3 bath kits & the ones using Bleach and Fixer. That's from long experience of using Chrome 6 and the Tetenal kit.

Ian