You maintain and have control over your private key at all times. Of course, these other systems also require that you change your email address, which is not necessary when using MessageRx. There is nothing to download or install with MessageRx. All you need is a browser capable of SSL secure communications. In Embassy mode, you can attach any file to any message.
All attachments are also secure.
You are absolutely anonymous when using any part of MessageRx. Only your MessageRx User name is displayed to any recipient. No information regarding your identity, IP address, or any other information is ever transmitted with any message you send. MessageRx has an undelete feature. You will always know if a message has been read.