Yes, you'll need to create a Guusto account to be able to claim your gift and redeem for a merchant of your choice. This will also ensure you'll never lose your gift in a stack of messages, since you can access it anytime through guusto.com or the mobile app. Once claimed, all your Guusto gifts and merchant gift cards are stored within your Guusto account - like a digital wallet!
This also confirms for the gift sender who exactly has claimed the gift, and also ensures that gift senders are prevented from paying for gifts that go unclaimed.