You asked, so I'll answer. They are absolutely worthless!!! other than as a paper weight. On another forum..... we had sent a series of emails requesting track and/or dyno data from several manufacturers. Not one had anything showing they actually do anything. The gist of the response email content was that they may help in improving combustion theoretically, and all the data shows they do not decrease efficiency.
Doh, the same data shows they do not increase efficiency either. WTH?
Use your $$ on soemthin else, or if it is burning a hole in your pocket, PM me and I'll give you an address you can send me your $$ and I'll send you the same thing a TB spacer gets you.... nothin!