I actually had a horrible experience with KR.
back in December 2014, I am with AT&T and I ordered a set from KR, installed it prior to my trip to Europe.
The initial experience was ok, upon arrival, the SIM card seem worked, switched to uk carrier, but very slow, and app is buggy, keep flash quite ,KN actually kept directing me to instal some carrier profile on my iPhone 6 Plus, and I did couple times, ever since I did that, my phone started to act weird. Internet is very slow and congested constantly. On my last night in Uk, it finally killed my iPhone, my iPhone kept restarting and became red screened and never came back again. I had to restore the entire phone completely and remove the sticker.
I still had 6 days in other countries so I decided to sign up for AT&T passport services. Pricy but at least the LTE was super fast and consistent. I asked for partial refund for knowroamin and not intend to try it again.