I've been using Crystal retinal 3 for about 6 months, and am now using every night without any complications. I just ordered what I thought was the next strength up but have realised that I've skipped straight from level 3 to 10 without using 6. My fault I know - but not helped by the website I bought it from only offering 3 and 10 (so I assumed 10 was the next level up).
Am I going to struggle going directly into 10, even I phase it in twice weekly? Obviously the best way to find out is to give it a go but interested in what others think. The alternative would be to buy a level 6 as put the stronger one away for now.