Switchable Ballast

A friend asked me to clarify before making a purchase.

1. (I know it's a dumb question, but it's better to find out now than later.) Is a switchable ballast truly switchable or does it still require a conversion bulb when changing out?

2. What's the concensus on the 600W Galaxy Ballast? Is it reliable and as quiet as they say?

3. Is there a rundown on nutrient selection? The GH 3-part Micro/Grow/Bloom seems relatively straightforward, but what about the other things like KoolBloom, Floralicious, etc... It gives a description on the GH site about what each does, but how does someone actually choose which ones they'll be using?

Are some more important than others? (I can see FloraKleen helping with flushing)

Forgot to mention cab size is 8Wx3Dx7H. It can be divided into two sections (3x4ft each) , or one long section. 600W should be fine for 12 sq. ft., right? (It's not even really 12 since the framing took 8in off each dimension.)

will answer some of your questions.
1. a switchable ballast will run either hps or mh bulbs all you have to do is install wich bulb you wich to use, some conventional ballast will also have a switch to select for mh or hps and this goes for most wattages with the exception of the 600 watt light, wich ive not been able to find a standard mh bulb available for the 600, there is plenty of mh conversion bulbs available for the 600 though, but wouldnt neccassarly buy a digital ballast that will operate both when standard bulbs are not readily availble.
2. dont know
3. gh 3 part is very popular and you can do a search if you want more info on it, and you can have great results, without using any of the other bloom additives, but you can try them if you wish, but in most cases it doesnt help and can even cause problems.
and a 600 would cover 12 sq ft

Thanks for the heads up on the 600W. Almost bought a switchable ballast with nothing to switch to. Any recommendations for a reflector and switchable ballast to light a 3x4 space? 400W seems too low, and 1000W seems too high.

the 600 would be the best choice for that space despite having to use mh conversion bulbs you could use a 1000 also but it will produce more heat so make sure you have good ventilation.
you will want an aircooled reflector whether it be a cooltube or regular air cooled reflector.