I'm having some trouble using the bottle warmer I got for my second baby. I had the Avent one for my first, but could never really get it to work right. I saw the Doc Brown's was really well reviewed, and I know a mom who loves it, so I got that one hoping it would be easier. But I'm having trouble thawing frozen breast milk, and heating milk in off-brand bottles (nuk, munchkin, etc). Anyone have any tips or tricks for using it with non-brand products??