We've been printing custom soft jaw inserts for our Kurt vises for years now. It's way cheaper than buying aluminum blanks and faster to make. For one-off parts, a printed jig is often the most cost-effective solution.
Hold on, doesn't the plastic just crush under real clamping force? For anything beyond super light duty, a printed insert seems like a false economy. You'll get creep and lose your grip, maybe even wreck the part. Machined aluminum is repeatable and solid every single time. The extra cost buys real peace of mind.