The pack consists of a four-exit exhaust for a noticeably fruitier noise and a barely noticeable 3-4bhp. Bigger wheels carry 225/40R18 tyres, of stickier compound.
For comparison, standard are 215/45R17 - actually Prius tyres, made for durability and low rolling resistance, not grip. A carbon-fibre strut brace stiffens the shell. An aero kit is effective but not too brash.
Out on a track, the TRD car has a neutral-to-oversteer steady-state cornering balance, as does the standard car. But there's a whole lot more grip. And it runs out less gradually, less transparently. Which is perhaps less fun. Mind you, the car I drove had optional adjustable dampers and stiffer front anti-roll bar. Still, the extra precision is nice. You're far less likely to get it sideways unless you've gone in fast. Which I didn't at first, because this car also had £8k's worth of mega-brakes. But I'm not sure the balance of lateral grip to power is as delicate as on the standard car (Tada is working on a lower-ratio rear diff, which would help). The playability is eroded, and with it the thing that makes the base car so unique.