IP-Relay (the web version) uses SSL. Your connection to relay is encrypted and is just as if not more secure than 711. SSL is the same kind of encryption e-commerce sites use to process your billing information.
To use 711, you need a TTY, a VCO device or to have your computer setup as well as a phone line. To use IP-Relay you just need a Computer and Internet Connection which is more and more common these days even in some cases not even having a phone line but just a high speed data line.
TTY's tend to be based off 50 baud Baudot, because it handles line noise well and tends to work even with the crummiest connections. The downsides: It's slow, It's half duplex (only 1 person can talk at a time).
