I've had both.
The foil highlights were beautiful!! And my hair didn't break off from them at all. Then about 9 months later I got it done again, and they used the cap method. Well, I dont know if they used too much peroxide or if it was because the previously highlighted hair was being bathed in peroxide again, or what, but my hair broke off terribly from it!! Three months later, my hairline was all broken off, and I had (& still have!!) a patch of hair on my crown that's shorter than all my other hair.
Also, if you have highlights, you have to be SO careful when you do your relaxer touch-ups that you don't overlap onto the highlighted strands, cuz they will break right off.
After they did the cap method, that's exactly what happened cuz pretty soon you couldn't even tell my hair had been highlighted cuz all those pieces were GONE!! I'm staying away from highlights from now on!!
I don't mean to scare you; just be aware... if you're going to do it, I'd recommend you don't go too light. The less peroxide, the better. I would imagine that the home highlighting kits probably don't contain the same amount of peroxide as what they would use in the salon.