Jerry,
There are 2 main differences between the two units. First the Roadmaster unit does not have a protective cover over the shaft to reduce seal wear and Safe-T-Plus does. The other difference that I am aware of is that Roadmaster has a 1 or 2 year warranty, and Safe-T-Plus has a lifetime warranty.
I have a Safe-T-Plus unit on my coach, but the main reason that I chose it was to get the optional trim unit that Henderson's Line-Up sells to go with it.
Gerald