Hi,
1. It's not duplication ; it is a javascript library which replace the display of the dropdowns but it looks like there is a little issue in the hiding of the original dropdown.
2. There is an option in HikaShop to display or hide the "product code".
3. For HikaShop ; we do not have special recommendation.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.