I hope you purchase goes well.
I ordered the same set through aliexpress - all appeared to be well but then I started receiving odd emails from the seller...telling me that they are not sending it via DHL as their website said, that it would be through Hong Kong post but they wouldn't register it because it would be a red flag to customs. To their credit, aliexpress must monitor the emails because they froze the sale and determined that this was a fraudulent sale. After about 12 days, my money was refunded. That's the good thing about aliexpress - they hold the money in escrow and don't give it to the seller until the parts are delivered or you file a complaint.
I don't know if this is the same seller that I ordered from - hopefully not. If you are successful in receiving the retracts and that they are decent quality, I might consider them again. In the meantime, I am trying to build my own.