The natural wood pattern rosette and satin finish make this a truly beautiful instrument for the both beginners and ukulele enthusiasts alike. Cordoba 15CM Concert Ukulele. 20TM Tenor Uke. The Cordoba 20CM is a concert size ukulele that features a solid mahogany top and mahogany back and sides. The natural wood pattern rosette and satin finish make this a truly beautiful instrument for the both beginners and ukulele enthusiasts alike. The reason I am writing about this Cordoba 20CM Concert Ukulele after Cordoba 15TM and Cordoba 15CM is that this is a special ukulele. The reason it is special is that it is a high-end beginners ukulele. Protege U100CM. 15TM Tenor Uke. 15SM Soprano Bundle. 20CM Concert Uke. The Cordoba 20CM is a concert size ukulele that features a solid mahogany top and mahogany back and sides. Here is the Best Cordoba Ukulele. Comes with Aquila Nylgut strings.