I've used one. For a while, the mags definitely put me at a disadvantage going against 10-round AI mags. Even now, my max is 10, while AI guys can buy +2 extenders. When I have a prone stage, the 10-round mag length doesn't get in the way, since I have a rear bag under the butt, but if I'm prone and a stage requires a mag change, I have to lift the butt to clear the mag because it's so long. Ever been on one of those stages that calls for 12 shots, so you had your ten-round mag and kept 2 in your SAP holder on the side of your rifle? You could quickly grab one, throw it into your ejection port and just slam the bolt closed on your regular rifle? Yeah, on the DT, that's not so simple. I had to insert the round past the barrel extension to single feed. If I didn't start to seat the round in the chamber, I was screwed because digging a round out is difficult and time-consuming, or I'd have to drop the mag, which is time-consuming. Honestly, it was just safer for me to do a mag change because if I screwed up the single feed, I was going to time out the stage trying to fix it. As mentioned, your face is in the way if shooting offhand. Thankfully, I didn't run into too many offhand stages, but it didn't really bother me to shoot offhand.
I'm sure I'm forgetting a few other minor issues, but that's not to say it was a bad rifle. It's very well balanced and compact, but there have been times I've felt a stage was better suited to one of my other rifles, but I've also had stages where I've done really well because I've had the SRS. It's certainly a viable option, but I think certain chassis (chassises?) are better suited to PRS.
Edit: I've never had a reliability issue with mine, and I've run it hard in windy, dusty, gritty, wet, snowy, whatever conditions. I've seen other rifles go down because it was super windy and dirt/dust/sand/etc was flying everywhere, getting into actions, triggers, and chambers. The SRS kept going hard.