roll bar extension

[limoncello]

I recently saw an ad for a roll bar extension - looks like a straight bar that attaches across the 2 behind-the-seat-bars. Anybody tried this setup? Is it a bolt-on? Drilling required? Does the top still work properly?
If it is easily installed and removed, it could be a nice track day addition. But somehow, from the physics side of things, if it's a quickie bolt-on does it really provide any true increase in roll protection?
My thoughts were (a) does it increase the height & protection (I'm tall, and with helmet even taller) and (b) it provides an attachment point for a 4 point harness should one want to go that route.
Open for comments...