I have these, with the solid blue handle. I haven't had a single issue with them. Once I thought I saw a line, but I am sure it was just because I was obsessing. This also happens to be the exact same type my doctor's office uses, so I figure they can't be too bad.
The only problem I can think of is that sometimes they take a long time to read, so let it sit for at least 5 min, 10 minutes would be better.