If you can't get him to blow either of the calls prior to purchasing one or both of them, you can go to their websites and listen to sound files of them to get an idea of how they are "supposed" to sound when used correctly.
Echo -
http://www.echocalls.com/soundfiles.html - click on the sound file labeled "Poly Open Water DR"
RNT -
http://www.rntcalls.com/products/items.aspx?id=11 - The RNT call in the link you posted is called the Duck Hunter. This is a link to the sound file for it.
Both of these calls are top notch beginner calls. If he is looking at getting both of them though, then I would prolly tell him to go ahead and buy the RNT, but to select a different Echo as both of these calls are loud. I'd tell him to look at an Echo Timber Poly in double reed. They'll run about $15 more than the Trash Talker, but they are quieter and would give him a little more variation between his duck calls. Good luck. RNT and Echo are hard to beat.