I've been a DR Hi-Beam user for years - love 'em. I thought I'd try a set of the Hi-Beam Flats on my Roscoe fretless 5-string and bought a set from The Perfect Bass (you can get them there or at least you could 6 weeks ago).
I was expecting a nice, bright flat with a lot of "zing" like I remember ground-rounds to deliver. But no! These are very thumpy with a very rapid decay, just like a traditional flat set, I guess. Not that this is bad, but it's not what I wanted. Anyway, they're off the bass after less than 6 hours of playing time, and I'm trying to decide what to do with them! Maybe a trade for something on the Buy and Sell forum.
Very smooth and silky to the touch and definitely well-made. I found them to be much higher in tension than regular Hi-Beam rounds, too. But definitely not the string for me.