This was a hotly debated topic when the VTR with the triangular barrel was first introduced. We bought one, in .223.
I can tell you this, Remington would not have done it without serious R&D.
Those that purport it's detrimental to barrel harmonics, expansion/contraction coefficients, yada yada... is just B.S. I can find engineers on the other side of every one of those arguments.
I believe it is a marketing gimmick.
I have seen no indication of the triangular barrel affecting accuracy, one way or the other, like Warbird says. But unlike Warbird, I like the look of the triangular barrel.
Absolute tack driver once we got it out of the crappy plastic factory stock, and into a B&C Medalist with a Timney...