Currently the only way to obtain Retainer information is to select an individual client and then drill down into that client's info ( a minimum of 3 clicks) to see if the client is using a retainer and, if so, what the current retainer balance is.
Please add to the Summary filter features the ability to show which clients have established a retainer and the current retainer balance.
On a related note, provide a summary filter to gather information on any Clients which have surplus payments on record in Studiometry that are NOT in Retainer. The ONLY way to discover that kind of surplus payment is to create a new invoice, at which time Studiometry gives notice that there is a surplus for that client.