I did a one gel nails course with gateway... It doesn't came anywhere near some of the other ( qualification ) courses I have done, but is good compared to some of the other one day courses around.
I would never recommend a day course if you don' have some experience already in that area, and be prepared to have loads of people lined up to practice on. I think tutors do say you can contact them with any questions, so use this back up if you need to.
I would say if you tend to lack confidence ( as I do sometimes ) you will need more than a day course.
As for my gel nail ability? .............hahahaha, - but then I don't have any other nail qualification even though technically I'm certificated and insurable through the guild. I think if I allreay had loads of manicure clients and lots of models lined up I might have got somewhere.