The original design sucked for power when it first came out.
Now they offer many good options and designs that are far better for airflow. The money is well worth it if the benefits from a positive displacement blower is what you are after. I know several people who are very happy with the TT set up.
1998 Roush: M112'd Aluminum block 4.6L 2V 6 speed track car
1999 SVT: Mostly stockish
1970 Mach 1: Resto-modded monster
2000 Roush #5004 - World's FIRST M112'd V6 Mustang. Sold, but not forgotten.