Anita, I hear you about not needing the monthly commitment but I am more aware of security issues with client files. Places like Drop Box, Google Drive and others are not secure for transporting client files. I am using eCourier which is a fully secure encrypted service that is easy to use and with no cost to your clients. You can send to as many people you wish and they can reply with no additional costs. This is a Canadian company with a service designed to meet the needs of the privacy issues for all provincial and federal bodies. I think you need to be concerned for the security of the data being transported. 

I also use eCourier.  Have been for several years and it's well worth it.  Secure way to send/receive files plus allows sending of large files.