The #5 STM mouthpiece plays and sounds great. Just like the Link STM Tenor m/p, this Bari m/p has a gutsy earthy sound.
As expected from Yamaha this m/p works very well indeed. The cost of the m/p itself is very reasonable, but the cost of the Yamaha lig and cap is a bit steep (cost nearly as much as the m/p itself) and not always available. Dawkes fixed me up with a BG L15 leather lig and cap set which works well with the m/p.