Preformed ponds have their uses IE if you can't dig very far down or want something very small. Many people get started with preformed ponds and add on to them later. Getting a performed pond level can be a real pain. Don't put koi in anything preformed or not if it's under 500 gallons, they won't be happy or grow well and may even jump out of shallow ponds. Liners allow for more creativity and are easier to install. Let me know if I can answer any more questions, Gail