Technically taking it alllll down is hogging, and roaching is shaping it to have an arch, like fjord's manes are often done. I love roached and hogged manes, my whole life I had horses with awful manes and longed for a nice, lovely long mane. Finally got 2 with nice manes and I constantly want to cut them off but am torn between long mane or no mane, ha! Anyway, it's perfectly fine to do it with scissors, however it might come out a bit uneven and messier and it sure takes a longer time to do it. (depending on how thick the horse's mane is) The growth usually doesn't take that long, honestly.
Here's some pictures of the palomino mare I used to have and her roached/hogged mane adventures.
Before: (She was a rescue sort of deal so excuse her initial condition, that was a work in progress.)
A week or so after the roach:
When I first did it I left about an inch of hair. And of course the wither patch and forelock.
About a month, maybe 2 after the initial hogging:
I don't have pictures of the full growth process but a shortly after the entire back half of her mane started flopping over, while the front stayed up. It drove me insane so I ended up cutting it all back down and on and off cutting it and letting it grow over the next year.
The flopping, about 2-3 months after the roach.
And this was about a full year later, though keep in mind at some point in there I did completely cut it down again (don't remember exactly at what point) but didn't cut it at all over winter november-march and it looked like this in march.
I did mine with scissors. I loved it, no up keep really - other than the occasional trim -, no hair all up in your hands and reins. I like the look, though a horse with a better neck would have pulled it off better than my mare. I got hooked though and now have to live with the constant battle of 'ugggggh I want a roached maaaaaane but they have such nice manes' There was no such 'nice mane dilemma' in the palomino mare's case. -sigh- I sometimes hope they might rub out a chunk of their manes in the night to give me an excuse, ha. Also I will add that the mare didn't seem to have any more or less problem with flies etc with no mane than the horses that did have manes.