The QA1 arms aren't longer, they "add travel" because they have a shorter vertical profile than the stock arms. This gives you about an extra inch of travel before the LCA hits the frame.
As far as lighter, they are. As far as stronger? Depends on who's doing the welding. I had a set of CAP tubular LCA's on my Challenger, right up until I broke one of the welds.
On further inspection, the weld that broke was extremely cold, no penetration at all. It was then ground down and powdercoated.
Which is probably why CAP sold out.
QA1 bought the CAP design. The design is sound though, and after purchasing a set of the QA1 tubular LCA's for my Duster I can say the welding is MUCH better. Like I'm not afraid to run them better. That said, after I inspected the old CAP tubular LCA's I came to the conclusion that there were two gussets that could be added that would seriously improve the strength of the welded joint that bears most of the load. I'm going to the adding those gussets to my new QA1 LCA's regardless of the improved welding. As far as voiding my warranty, even the CAP arms lasted well over a year, so I'm not worried about it.