That's actually my front line mod that I learned from Jeff Weiss about 7 years ago. I have been using it for a long time, mainly to self land. Bob, Danny, Tom and a few others have modded their bars as well.
It doesn't do much good to hook to it while riding (unless you never unhook or do tricks) because it will turn into a tangle ClusterMuster with multiple rotations or when you unhook it may place pressure on the front line (leash gets lengthened to ultimate distance... then pulls on line), possibly accidentally steering the kite quickly (that's really bad). That particular mod is really only useful for self landing, imo, and I use it a ton for that.

After having said that, if the winds go ballistic while I am on the water, I do switch over to that front line with my leash as a flag out system. In that scenario, I would get about 50 yards from shore, flag it out, and then drift in after the kite is in the water (I am talking nuking, problem winds). It definitely kills and flags out the kite, I have done it many times.
The problem with doing this is the other lines are now slack and may tangle around you though. That's why I try to do it offshore (I still believe a little distance from land is good), but close enough to shore that I will be in the water only a short time.

Anyway, it's not a real option to attach to the front line OS in my opinion while riding, unless a beginner (then I think it's a great option).
I still would have had to QR by the way the other day. It wouldn't have mattered at all where my leash was.
I may not have had to release the secondary leash QR, but again, attaching to the front line OS affords more difficulties than solutions when unhooking and doing multiple rotations, so I don't view it as an option. If I did, I would hook my leash there all the time.

I have tried to figure out how to get a line to run from my front line OS down through the bar (to avoid tangles and the distance problem).
The SS Rev system seems to be the best approach at this. I mimicked that approach, but I personally decided against having all that "free" line in the water to tangle me up every time I release the kite. To each his own, no approach at this time is without flaw (unfortunately).

The new Best bar has front line OS handles on both sides btw, they put them there for self landing.
Supposedly they are going to make a vid or picture essay showing how to use them.