First, they make a mess. I had so many smudges I had to wipe away and my blue pen started running dry while I was still on my first hand, so I had to really work it and ended up with ink all over my hands. It also runs a bit on the nail which is another reason complex designs don't work so well. I wanted crisp edges and got rounded corners instead. Another problem is, as I previously said, the blue pen started drying up. I'm not sure if it's a common problem as the white one seemed fine the whole time and I was using it more. I never left them uncapped so they may not have a very long life.
So far I'd only recommend them if you find them on sale (I got them buy one get one 50% off at Rite Aid) or have a high value coupon but I plan to do a part 2 review once I've given them a second chance with a simple flower or heart design. I also suspect practice helps as well but overall these are best for simpler art. Now for the pictures. The first is the Bavarian flag I was attempting. The others are my results.