PowerShell: Copying Only Files From a Folder

Function (snippet):

function copyOnlyFiles{
    param(
        [Parameter(Mandatory=$true)][string]$sourceFolder,
        [Parameter(Mandatory=$true)][string]$destinationFolder
        )
    $totalSizeBytes=0;
    # Get-ChildItem "C:\Temp"|?{!$_.PSIsContainer}|%{robocopy "C:\Temp" "C:\TempCopy" $_}
    # Get-ChildItem $sourceFolder|?{!$_.PSIsContainer}|%{robocopy $sourceFolder $destinationFolder $_}
    # New-Item -ItemType Directory -Force -Path $destinationFolder | Out-Null
    #$duration=measure-command {Get-ChildItem $sourceFolder|?{!$_.PSIsContainer}|Copy-Item -Destination $destinationFolder}
    $duration=measure-command {        
        $filesOnly=Get-ChildItem $sourceFolder|?{!$_.PSIsContainer}        
        $filesOnly|%{$totalSizeBytes+=$_.Length;write-host $_;robocopy $sourceFolder $destinationFolder $_}        
        }
    $totalsizeGb=$totalSizeBytes/1GB
    $totalMinutes=[math]::round($duration.TotalMinutes,2)
    $gbPerHour=[math]::round($totalsizeGb/(($duration.TotalMinutes)/60),2)
    write-host "-------------------------------------------------`r`n$([math]::round($totalsizeGb,2)) GB completed in $totalMinutes minutes. Speed was $gbPerHour GB/Hour."
}

Sample Output:

PS C:\Windows\system32> copyOnlyFiles -sourceFolder c:\iso -destinationFolder C:\isocopy
New Text Document - Copy (2).txt
New Text Document - Copy (3).txt
New Text Document - Copy (4).txt
New Text Document - Copy (5).txt
New Text Document - Copy (6).txt
New Text Document - Copy (7).txt
New Text Document - Copy (8).txt
New Text Document - Copy (9).txt
New Text Document - Copy.txt
New Text Document.txt
Windows_Server_2016_Datacenter_EVAL_en-us_14393_refresh.ISO
-------------------------------------------------
4.76 GB completed in 0.42 minutes. Speed was 927.63 GB/Hour.