The Beansprout Banjo is available in either Concert or Tenor Size. The only difference between the two is the scale length (the distance from the nut to the saddle--this distance determines the spacing between the frets).
The concert has a 14.72" scale length, while the tenor is 17". The two sizes share the exact same rim & hardware. When choosing your custom ukulele, you should take into consideration acoustics, comfort, and playbility (primarily affected by fret spacing). There is no right or wrong answer.