Hi,
When I called Amoscos the other time, they gave me the contact to partytime and told me they are their associate company...whatever that means. i have been buying from partytime since. Maybe cos I buy in cartons so the price is cheaper. If you buy individually, they have adjusted the price and now, you are right, the BP price is cheaper.
I usually buy in carton (they can mix the flavour anyway) then keep lor cos quite handy leh. just keep in freezer and serve whenever there are guests or I feel like snacking...haha.