Great that your son wishes to learn to play the banjo as learning other instruments can expand his musical playing skills.
As for beginning banjos to play, much depends on what type of music he wants to play. 4 string banjos are used to play dixieland and jazz. 5 sting is used to play bluegrass. 6 string banjos play like a guitar but are more advanced and might not be the one that your son should start off with first.
As for what to look for when purchasing a banjo for the first time, it should have strings that are easy to push and playable. They should also have a good sound. As for brands in which to look for, see about going to your local music store and look at companies such as Deering, Gibson, and Fender. From reviews I have found, both the Deering Goodtime Special and the Fender FB 58 are good banjos to start off with.
Visiting your local music store and trying out some of the instruments would be the better choice than purchasing online as not being able to give it a look over before playing.
I have looked at the two you have listed tonight and the first banjo from Jameson would be a great instrument for a beginner. It has solid reviews and those that have started out playing recommend it. The price is quite good and Amazon has a good return policy. The price is under the price range you wish to spend and free shipping is an added bonus.
The banjo offers many features found on more expensive models, such as the tuner. It looks very well built and should offer your son many years of playing enjoyment.
You are very welcome as I am sure your son will enjoy this instrument for many years. If you could please take a second to rate my assistance so that I can receive credit for helping you today.