Differences in specifying connection between conversations and messages

[dantasfiles]

In this sample app, in order to display the messages of a conversation, a "getConvo" query is used, which returns the conversation and its messages.

type Conversation 
  @model (mutations: { create: "createConvo" }, queries: { get: "getConvo" }, subscriptions: null) {
  id: ID!
  messages: [Message] @connection(name: "ConvoMsgs", sortField: "createdAt")
  ...
}
type Message @model(subscriptions: null, queries: null) {
  id: ID!
  conversation: Conversation! @connection(name: "ConvoMsgs")
  messageConversationId: ID!
  ...
}
type Subscription {
  onCreateMessage(messageConversationId: ID!): Message
    @aws_subscribe(mutations: ["createMessage"])
}

However, in many of the sample apps from @dabit3 , like conference app in a box, he uses a different style of getting messages, with a "listMessagesByConversationId" query, and a keyfield on the connection between conversations and messages

type Conversation @model {
  id: ID!
  messages: [Message] @connection(name: "ConvoMsgs", keyfield: "messageConversationId")
  ...
}
type Message @model {
  id: ID!
  conversation: Conversation! @connection(name: "ConvoMsgs", sortField: "createdAt", keyfield: "messageConversationId")
  messageConversationId: ID!
  ...
}
type Query {
  listMessagesByConversationId(messageConversationId: ID!): ModelMessageConnection
}
type Subscription {
  onCreateMessageWithId(messageConversationId: ID!): Message
        @aws_subscribe(mutations: ["createMessage"])
}

Is one method more efficient than the other in cost or speed, or are they very similar?