Is there any benefit/drawback to booking vueling flights through ba.com? Seat bookings (I am ggl)? Checked baggage?

Planning for lgw - bio in early July (2 adults /1 infant)
Vueling give me an option to either go HBO (small bag under seat/checked cabin bag) or almost twice the price for the family option (full checked luggage / seat reservations etc).

it is not clear to me what I get if booking with BA... I presume only baggage under seat and 10kg checked limit?

Your baggage allowance per person

• Gatwick To BilbaoHand baggageVueling allowanceChecked baggageAdult, Young Adult and Child: 1 checked bag per person included (Vueling weight restrictions may apply)
  Infant baggage allowance: 1 checked bag (Vueling weight restrictions may apply)