Not sure how permanent it is - I've been using NB for the past three months but have missed days in between.
I went 7 months without using Brava and retained my growth

After that I used Brava two more cycles, then BB for two, and now NB.
BB gave me Brava size swelling however it was very painful for the first while, until I could get used to it

I used NB for an hour this morning and am still retaining about a half inch of swelling! This is the first time I've used it in 2 weeks.