Pros: These are good quality for the excellent price.
Cons: I do feel that the wire is a little too thin. The 3.5mm device you will connect to this will have a considerably heavier wire. The 2.5mm sized cable will undergo excessive stress supporting the weight of that 3.5mm jack and the larger wire. I know from experience that someone will have to be careful with these adapters or they will wear out quickly (internal wires will fray).
Summary: For the cost, these are worth the cons, and I bought a few of them at once. They arrived fairly quickly and packaged in a tough little bubble wrap envelope. These are perfect if you are not using them for a light set of earbuds, if you are going to connect headphones with a thick wire, I suggest you go for the more expensive block type adapter.