Having only flown the 139 in Africa, I don't know anything about it's deicing capability, but more than a decade offshore out of Eastern Canada, half on the ole S61 and half on deiced Super Pumas, I can certainly say my stress levels reduced by a good 80% with the deiced Pumas! Sure, we flew in much worse weather than we would have with the S61, but the system was more than capable, and the stress of getting caught out in icing, due to poor forecasting mostly (were talking 200 miles out), especially at night, and the odd low level scud run to get back in trying to stay out of cloud, was gone. IFR all the time, and plenty of options available that weren't there with a non-deiced bird.
Highly recommended, if the system works as advertised.