From six months on, except for water work and the show ring, I use fur savers exclusively.
Combined with proper body mechanics it is just as effective as any other collar. In addition it gives a gentler correction than a more conventional choke collar. Proper body mechanics involves using a double handled leash and pulling to the side (same concept that allows a person to take a horse around on a lunge line), making the fur saver as effective as a head collar (like the gentle leader) without making your dog look like he is muzzled, without irritating his face and without risking a whiplash injury.
I fit the Newfs like you would for a regular choke. Normally this means putting it on one ear at a time, same for taking it off. Like to have three or four links when you pull it tight. Pop works much better with the larger links.
There are two types of fur savers, the ones with end welded links and those with centre welded links. You should get the latter as they are stronger.
If ordering a fur saver, it is important to know that they are measured for length differently than an ordinary choke. Regular chokes are measured from the inside of the end rings whereas fur savers are calculated in length from the outside of the end rings. Most adult Newfs use a 24 inch or 26 inch collar; a few may require a 28 inch.
The biggest advantage of a fur saver for a Newf, as the name implies, is that it does not wear the fur around the neck. This is because the elongated links are less likely to get caught in the fur compared to other types of chain collars (whether chokes or martingales). Not only does the catching in the fur tear the fur but it also causes unnecessary discomfort.