Hi Taro,
 
I just wanted to write a little note to let you know a couple of things.  First, I love my bass, and am finding that I play it more than my Upright Bass!  Second, I thought I'd share something with you.  I had my neighbor, who is a machinist, cut a groove on the backside of my BEF2 bass extender (see picture).  The reason is that it's a perfect place to hide an Apple AirTag, which will help me keep track my bass in case it gets lost or stolen.  The groove is 3.5 cm deep and 3.5 cm long, and .95 cm wide. An AirTag plus a small rubber spacer fits perfectly in it.  I thought I'd send it to you in case Yamaha ever asks for feedback from your customers about their instruments.
 
Best regards to you and your family,
 
John
(Purchased item: YAMAHA SLB300 Silent Bass)