They're excellent. When I got mine years ago, I did side-by-side testing of standard, and modified rounds. All the ammo types I was using at the time. I don't think I kept all of those targets, and don't concern myself with it regardless. I mostly use different ammo types these days.
What I remember is this-accuracy either stayed the same, or improved marginally. Mostly stayed the same though. For me, the main goal was to make huge hollow points out of CCI Blazer ammo for pest control. Works incredibly well. I also took some unmodified Blazers out west to compare. Shot gophers with HPs, then switched to solids for a few mags. Dramatic difference. The outcome for the gopher was ultimately the same, but the speed with which it dispatched them was very different. Large HPs in those Blazers really rearranged gophers, a "bang/flop" over 90% of the time. An audible "thup"/slap sound. Solids-definite, and obvious difference. I know there are some tender types who read these threads...so I won't expand on that.
Glad I have one, and enjoyed the brief phone conversations I had with Neal getting mine ordered.