I've never heard of this "f1" brand, however, i bought my sachs oem clutch kit from gripforce-clutches, good transaction.
This includes a lightweight flywheel for 450$, that's a good deal. The lightweight flywheel is single mass, but i believe most aftermarket ones are.
Hot: 2001 Estoril M Roadster
ZCP 19's, ZHP knob, JL 8W3
Cold: 2002 TiAg M3 6mt
ZCP 19's supersports, ZHP knob, UUC short shift GROM, OEM 18's w310's,
http://absolutehid.ca hid kit