I am a level 3 hairdressing student and I can honestly tell you that most box dyes are horrendous. Most of these products, Xxl live colour, Casting creme gloss, belle colour, nice and easy, to name a few - contain metallic salts. This can have violent reactions with the hair when subsequent products are applied. I.e intense heat, fizzing, discoloration of the hair, not to mention chemical burns. Also the peroxide levels used in many home kits are a lot higher than professional colors, which can cause damage to the hair and scalp. Another problem is the application technique people tend to use. Most people using home kits tend to have a slap it on approach, causing banding of colour, build up on the mid lengths and ends of hair and breakage.
Word around the industry at the moment is that Olia, which is marketed by garnier who are owned by loreal is the repackaged original formula of Inoa - this pro colour was rejected by most salons due to poor coverage, low cost effectiveness and severe damage done to clients hair.
Id say where possible please go to your local college, most are crying out for clients, you will get a professional job done at a fraction of the price 
If However you choose to go for box dye, please please do a skin test 48 hours prior and a strand test to check the result 