These mugs are really nice. They have somewhat heavier glass than is usual in borosilicate glass which should contribute to longevity. The double wall construction works really well at conserving the heat of my coffee. They also work great for boiling water in the microwave for tea.
I did have a problem where liquid started pooling between the inner and outer walls of one mug, indicating that a tiny crack had developed. I contacted the company. They apologized and immediately sent out two new mugs. I thought that this was great customer service since I only reported the problem with a single one.
These have become the go to mugs for coffee and tea for both my wife and myself and I heartily recommend them.