Opening Sword & Shield Single Blister Pack [Gossifleur] returns about $4.04 in card value against its $14.99 price — roughly $0.27 back per dollar spent. On current prices, you lose money on average by opening it.
See every card and pull rate in Sword & Shield Base Set
How expected value is calculated — card value only, from published pull rates and daily market prices.
Sword & Shield Single Blister Pack [Gossifleur] on TCGplayer