I used them when the first came out around 1976, and used them off an on until about 1982. I finally decided that for me, I'd rather have flats for what they do, and rounds for what THEY do. All the modified rounds I've tried over the decades (D'Addario in the original nickel as well as the stainless ones, GHS Brite-Flats, and Dean Markley Groud-Roundwounds) have the same issue ultimately- they combine what I find to be the worst of both worlds, not the best.
Your mileage may vary... And, BTW, I liked the GHS Brite-Flats better than the either the D'Addario or the DM, and I'm a huge fan of D'Addario strings.
John