Whether you need a 2nd uth on your cool side will really depend on the kind of ambient temps that the room has. If you are from a warmer climate you may not need the 2nd one but if your enclosure is located in a room that gets cold you may. The ReptiTemp will not allow you to set two different temps.

I personally have not used the 500R but have heard mixed things about them. Ranging from they work great and have for a long time to it getting stuck into an on position and almost harming snakes.

I'm not sure what kind of budget you are working with but there are some very realiable thermostats. Ranco and Johnson on/off thermostats have been used in this hobby for a long time and they work great. A step above this would be a helix or herpstat proportional thermostat.

Here is a good FAQ to thermostats...

http://www.reptilebasics.com/Thermostat-FAQ-sp-10.html