I also have the M-class, and the authentic Xvostick...I like both, but the Xvostick I use a tremendous amount more. The side-by-side factor really makes it that more pocketable, it's just so conventient in the hand and to take with you, the M class is quite tall, and a
tank on top makes it a bit too tall for me, hence I do not use it that much anymore.
That being said the Ystick is however quite a bit bigger than the Xvostick, still for me nothing beats the side-by-side form factor so I went for the Ystick....two actually

$159,- was a great price for a
mod with this chipset. (they are now up to $179,-, so if you are still contemplatig them I guess you should decide soon).