I can't tell you about their performance in the S61 in particular, but I used them on every flight for the last 9 months and I am still in love with them, never felt the urge to go back to my Zulus (which I liked a lot at the time). So far I tried them on R44, C206 and C208 and have no complains.
I was very hesitant at first, too, but after reading a great review by another helicopter pilot I took the plunge. It was the very first time in 6 years that I was able to get out of the cockpit after more than two hours of flying and not have a throbbing headache from headset clamp force or feel fatigued. They are so light that one tends to completely forget about them (careful on exit...). They also offer advantages in conjunction with using sunglasses and baseball caps: you can put on either one single handedly AND you won't suffer the usual noise increase from the stupid temple gap in the earseal.
The important thing is that you order the right size of ear plugs. They ship them with a handful, so ask them to include one of each size (S, M, L) to test before you go ahead and order a set of a dozen. I believe you can also have custom fit ear plugs made at your local acoustician.
If you have the money go for it, you will definitely not regret it!
BTW: call them up / write them an email when you order that you'd like them to put on the hardwired helicopter plug (+$40) but ask them to send the connectors for FW with it ($0). That way if you ever want to resell the headset it is simply a matter of 4 screws and 5 minutes to rewire them to FW if need be.