The main differences between the T3 and T7 are:
T3 has ABS casing, T-7 has metal.
T-7 is rated for commercial use.
T-7 can be used continuously, the t-3 i believe is 30 mins on, 30 mins off (or similar)
Both accept the same jigs, the t7 comes with more jigs however in the package to start...