F-one seems to have quality issues more frequently than other brands from what I see. There is a mention about Manera EXO harness hook snapping here on forum, I have seen f-one bar metal parts rusting after 2 weeks trip (http://www.kiteforum.pl/forum/viewtopic.php?f=4&t=73763). There is too much choice of other brands to gamble with one having quality issues imho.
It appears that something at the stopper ball eroded or cut thru both lines. I assume you checked the hardware at or near the stopper ball for any sharp edges. Also, I'd compare the new parts with the cut lines and make sure the new parts won't fail.
I do paragliding (still a newbie) and I can assure you that it is inconceivable that a company has issues in any of its products.
In kitesurfing it's a different story...
Same thing with climbing gear. If there is ever any sort of recall they make sure to reach all customers. With climbing gear, paragliding gear, work safety equipment etc, all have safety standard organizations set up with strict guidelines to follow. Kiteboarding equipment is viewed like a toy in comparison unfortunalty.
Found this on one site talking about safety standards for rock climbing...
more climbers, accidents, & $$$, lead to more attention to standards
• mid 60s, rope testing
• early 70s, UIAA safety commission • 70s and 80s, research & standards • 90s CEN, ASTM, etc.
research and standards effectively reduce “equipment failure” to zero.