Unless your a seriously hardcore track monkey i dont see where the benefit of throwing 700quid at such a thing will come from.
Afterall the fancy suspension does an excellent job of cutting torque steer and maximising traction on the Clio, quite frankly the most balanced (open diff) FWD car ive ever driven.
Yes it wiil improve with an LSD but you have to concider the day-to-day factor, as an LSD can get tiresome at low speeds. One of the points the Mk1 Focus RS got slated for all those years ago.
If your car is your daily driver, you could spend the money better elsewhere in my opinion.