import pandas as pd

def con_udatasets(datasets):
    """
    Concatenates the locator DataFrames of the given UnifiedDataset objects,
    and returns a new UnifiedDataset with the concatenated locator.

    The function checks if all elements in the input list are instances of
    the 'UnifiedDataset' class without directly importing it. It then calls 
    the `get_locator()` method of each dataset, concatenates them, and sets 
    the new locator in a copied version of the first dataset using `set_locator()`.

    Parameters
    ----------
    datasets : list
        A list of UnifiedDataset instances to concatenate their locators.

    Returns
    -------
    UnifiedDataset
        A new UnifiedDataset with the concatenated locator.

    Raises
    ------
    ValueError
        If any element in the list is not an instance of 'UnifiedDataset'.
    """
    if not all(ds.__class__.__name__ == "UnifiedDataset" for ds in datasets):
        raise ValueError("All elements in the list must be instances of 'UnifiedDataset'.")

    # Concatenate the locators from all datasets
    locators = [ds.get_locator() for ds in datasets]
    con_locator = pd.concat(locators, ignore_index=True)

    # Create a copy of the first dataset
    new_dataset = datasets[0].copy()

    # Set the concatenated locator to the new dataset
    new_dataset.set_locator(con_locator)

    return new_dataset
