I have both the X-metal and the BBK. I find each has its strengths. I have
never had either one hang or cause idle problems for me. They are very different in how they react to throttle input though. I have tested both on my car for more than 1K miles each and I much prefer the X-metal.
X-Metal TB
The x-metal TB makes the car want to buck a little when you press the gas (single blade design so a bit more air jumps in). What I mean is it makes the car jump off the line and I like that a lot. I like fast response from my right foot. The problem with that is if you have a daily driver or do a lot of around town driving it can get annoying when making light shifts. It takes getting used to but when you open it up the car reacts fast and just breaths like nothing else. The car feels stronger SOTP
BBK TB
The BBK is a cool looking TB and gives very similar response to stock. Easy for around town driving but you will not feel any gain or seat of the pants "SOTP" change from it. When you go WOT you don't feel any significant change in the cars reaction, power. It probably gives some hp gain at the top end but I couldn't say I felt much difference
Don't expect a lot of power from a TB but I can tell you my experience is the car reacts better with the x-metal and drives smoother with the BBK. Depending on your style of driving you have choices.
I hope this helps on making some sort of educated decision.