Observables vs Promises

Observables vs Promises.ts

/**
 * Promises
 */
    let selectedProduct = this.client.api( 'product', 'get',  {id: product_id} );
    let metadata =  this.client.listMetafieldByProduct( product_id );

    Promise.all([ selectedProduct , metadata ])
    .then(( result) => {
        console.log('result:', result);
    })

/**
 * Observables
 */
    let selectedProduct = Observable.forkJoin(  
        this.client.api( 'product', 'get',  {id: product_id} ),
        this.client.listMetafieldByProduct( product_id ),
    );

    selectedProduct.subscribe( (result) =>{
      console.log('result:', result);
    });