Ordered a Medium of this shirt, expecting it to be tighter than Medium button-up shirts typically sold in US stores, and this was indeed the case. The shirt is very tight and is a little short in the body and sleeves - again, this is expected and no issue for me as I only keep the sleeves rolled up and don't need to worry about the shirt tucking in. The material is light but otherwise akin to typical button-up shirts sold in US stores. The breastpocket is not actually a pocket, just a detail on the shirt.
If you're looking to buy and are from the US, you may have a more comfortable/less tight fit by going one size larger than you'd typically buy.