Implementing "df" as a Powershell script

Note that I first have 'DiskFree' which creates an object for each line, so that I can use it in PowerShell applets that need disk usage info in an easily digested fashion, then use the list of objects in 'df' to display in a formatted manner. This is all in my startup profile for PowerShell so I have it handy when I'm at the command line. This is an example of writing Perl-esque Powershell on the latest Windows 10. People who were weaned on Powershell back in the Windows XP days likely are going to be rather appalled because "it doesn't look like Powershell!". Well, Perl people don't like how my Perl looks either -- "it doesn't look like Perl!" -- I dunno, people who cling to inscrutable syntax just because are, well, strange. I'm more into clarity and simplicity of reading when it comes to my code.

function DiskFree($dir = "") {
   $wmiq = 'SELECT * FROM Win32_LogicalDisk WHERE Size != Null AND DriveType >= 2'
   $disks = Get-WmiObject -Query $wmiq
   [System.Collections.ArrayList]$newary = @()

   foreach ($disk in $disks) {
        # Write-Host "Processing " $disk.deviceId
        $used = ( $disk.Size - $disk.FreeSpace )
        $percent = [math]::Round($used / $disk.size * 100,1)
        $freePercent = [math]::Round($disk.FreeSpace / $disk.size * 100,1)
        if ( ($dir -ne "" -and $dir -eq $disk.DeviceID) -or ($dir -eq "")  ) {
           $dfObject = New-Object -TypeName psobject  
           $dfObject | Add-Member -MemberType NoteProperty -Name Device -Value $disk.deviceId
           $dfObject | Add-Member -MemberType NoteProperty -Name Used -Value $used
           $dfObject | Add-Member -MemberType NoteProperty -Name UsedPercent -Value $percent
           $dfObject | Add-Member -MemberType NoteProperty -Name Free -Value $disk.FreeSpace
           $dfObject | Add-Member -MemberTYpe NoteProperty -Name FreePercent -Value $freePercent
           $dfObject | Add-Member -MemberTYpe NoteProperty -Name Total -Value $disk.size
           $res = $newary.Add($dfObject)
        } 
        # Write-Host "Processed" $disk.DeviceId
    }
    $newary
}


function df($dir="") {
   DiskFree($dir) | Format-Table -Property Device,Used,UsedPercent,Free,FreePercent,Total -AutoSize
}