This is a great t-shirt, excellent quality, very comfortable, and it keeps you warm, but as advised, the sizes are very small, or at least the are very tight in a compression sense. I take an extra small in a regular t-shirt, ordered a small, and it's still very very tight. I don't think it's a bad thing if you are looking for compression-wear, but just be aware that you'll want to go up one to two sizes if you want a comfortable fit versus compression. Otherwise very happy.
A doctor suggested that for circulation issues related to heart and arthritis swelling I should try compression garments. These tesla products worked better than I had expected and I have better circulation and less pain. I'll be buying more of these since they are so effective in treating a variety of issues and they feel comfortable to be a second skin.