Thanks for your answer, I wasn't expecting feedback from Fiio staff
Sorry but this is not a good enough reason, I used Radsone ES100, it had dedicated buttons (plus optional functions on long press) for all these basic functions.
I know Fiio always choose to mitigate navigation buttons with vol buttons, but this is not convenient.
In fact this and the battery life of the BTR series always put me off, even if it seems that BTR5 is one of the best selling BT adapters, l agree...
Two more buttons can fit in such small device, no problem, of course it raises the manufacturing costs a bit, but not that much.
It is not that I don't like Fiio products in general.
I have FH3 and FH7 IEMs and for the price, in terms of sound they are a marvel to my ears. I recently bought the UTWS5 because of extremely good reviews, and I accepted the fact that you cannot put too many buttons on TWS units, but the connection is unstable; connecting/disconnecting is somtimes a hassle, and the battery life is way off the official figures; the adapters go off only after 3-4 hours...
When they work, the SQ and audio sync L+R, stereo imaging (which is quite challenge...) is great, I recognize the strong points of such a product.
I still criticize Qudelix for their wierd button implementation; lots of hit and miss...
But For the BTR15, if you would have just added these two buttons, plus a battery life of 10-15hrs, I would have give it a try, for sure...
But as I said before, maybe I am the only one, or one of the few that consider this as important.