I used this to activate a 3 nano sim in my iphone 4 before my iphone 5 turns up.
Works well and does not snag in the phone. I have had similar products that fit in the sim tray before where this has been the case.
It's important to note that the design of this is different to that of the one provided by O2 with their nano sims on Pay monthly contracts, both work but this one is superior. The sim is held in a more secure way, not just a push fit, there is more of a risk with the O2 adaptor that it the sim could pop out of it and jam in the phone.
Packed in an oversized cardboard envelope. It's so small for a second I didn't think that there was one in the envelope careful you don't loose it!