The mits I one fits top like a glove, also has the cut out slot for middle seat belt to come through. £155 ish fitted dear but even though my dogs are border terriers, 9kg in weight, Kinetic energy is around 4380 J of energy would kill dog and possibly whatever it hit inside.
A very small price to pay. NB once fitted, you need Allen key to remove side parts, one side only should do.