According to the link provided (and the Gruppe-M website), this model (FRI-0302) will fit:
*BMW Z4 (E85) 3.0 Convertible i Petrol RWD 2003 - 2005
*Alpina Roadster (Z4) 3.3 Convertible Petrol RWD 2003 - 2005
The link also shows that the claimed £970 retail price is actually £870 - and £740 from other suppliers (CA-Automotive for example).
At the right price, it could be a bargain for someone.