Converting Custom Object arrays to String arrays in Powershell

This will give you what you want:

$strArray = $ms | Foreach {"$($_.Option)$($_.Title)"}

Select-Object is kind of like an SQL SELECT. It projects the selected properties onto a new object (pscustomobject in v1/v2 and Selected.<orignalTypeName> in V3). Your second approach doesn't work, because $_.Option in a string will only "interpolate" the variable $_. It won't evaluate the expression $_.Option.

You can get double-quoted strings to evaluate expressions by using subexpressions, for example, "$(...)" or "$($_.Option)".