PrompForChoiceSingle.ps1

function Get-CommandChoice
{
    [CmdletBinding()]
    param
    (
        [Parameter(Mandatory=$true)]
        [Array]$Array,
        
        [Parameter(Mandatory=$true)]
        [string]$caption,
        
        [Parameter(Mandatory=$true)]
        [string]$Message,
        
        [int]$Defaults
    )
    
    Process
    {
        $Choices = [System.Management.Automation.Host.ChoiceDescription[]] @($Array)
        $Selections = $host.ui.PromptForChoice($Caption, $Message, $Choices, $Defaults)
        foreach ($Selection in $Selections) 
        { 
            $Array[$Selection]
        }
    }
}

$Extensions = @('Git','Pester','Psake','None')
$Caption = "Please select a single Option"
$Message = "This prompts like it should"
    
$CommandChoice = Get-CommandChoice -Array $Extensions -caption $Caption -Message $Message -Defaults '0'
$CommandChoice

PromptForChoiceMultiple.ps1

function Get-CommandChoice
{
    [CmdletBinding()]
    param
    (
        [Parameter(Mandatory=$true)]
        [Array]$Array,
        
        [Parameter(Mandatory=$true)]
        [string]$caption,
        
        [Parameter(Mandatory=$true)]
        [string]$Message,
        
        [int[]]$Defaults
    )
    
    Process
    {
        $Choices = [System.Management.Automation.Host.ChoiceDescription[]] @($Array)
        $Selections = $host.ui.PromptForChoice($Caption, $Message, $Choices, $Defaults)
        foreach ($Selection in $Selections) 
        { 
            $Array[$Selection]
        }
    }
}

$Extensions = @('Git','Pester','Psake','None')
$Caption = "Please select multiple Options"
$Message = "Having [int[]] instead of [int] for Defaults breaks prompt"
    
$CommandChoice = Get-CommandChoice -Array $Extensions -caption $Caption -Message $Message -Defaults '0','1','2'
$CommandChoice