Hi
I'm new to nails too. I am currently doing a college course in manicure and pedicure which is great. It teaches you, comprehensively, about bone structure, the skin, muscle structure etc., as well as mani/pedi proc but it also teaches you other treatments as well and their benefits. Such as paraffin wax, warm oil, mask with heated mittens/bootees. I've thoroughly enjoyed it as it teaches helps you uderstand how things can effect the skin such as the environment and different diseases/disorders of the nails. It's very thorough and you don't get your recognised qualification until you are competent and have the knowledge and understandig necessary.
I can't comment on any one day courses as haven't done any but I personally can't imagine that it goes into it as thoroughly in a day, plus with a longer course you have the opportunity to develop your skill in filing, cuticle work, polish application etc.
I've just finished my first two days of nsi foundation and what i've learned already at college will be invaluable when it comes to my written exam. The training so far has been great, very thorough and totally enjoyable. I have two fantastic trainers too which is also good. It is intensive though as i have a portfolio to build in the next couple of weeks and a written exam to revise for.
There's both ends of the spectrum there for you and each has it's merits. I guess it's down to how you prefer to learn yourself and how uch you want to know.
Sorry if there's any typo's in this, I'm typing left handed as i'm soaking off my nails from yesterday. Practice, practice, practice........ hth