i use cheapies for areas that arent high pressure, ie pre turbo intake,and are prone to less movement, but joins that need a lot of movement or are close to heat etc i use brand name ones for.
i had a cheapie and a brand name joiner side by side, and they physically feel quite different. also had a cheap one nearly melt right through due to being a tad close to something hot whereas the brandname one seems OK in that spot untili moved the pipes round a bit to get it away from the heat.
I only really seem to have real problems when running up over 20psi, or extended periods or raping.