Inserts have been around for some time. True Tempers Sensicore product was popular for several years and their new Elevate product is kind of the next generation product with insert technology that offers a “Vibration Suppression System”. The Prosoft Inserts will do the same thing. The purpose of these types of inserts is to reduce the low frequency vibrations that occur at impact in steel shafts. The vibrations can cause discomfort and, over time, damage to joints. Claims are that with the inserts vibrations are reduced to levels that are equal to or lower than even composite material (graphite), which has a natural vibration dampening component. This is the primary benefit.
As far as the affect on a shafts stiffness, there is no affect. Balance point or swing weight affect is very minor and totally dependent on the weight of the insert and the location. The difference that would be noticed will be the feel of the club. Some players say the feel is deadened (some like it and some don’t) and some say it makes the shaft feel softer (even though it isn’t). The benefits are worth it, in my opinion, as long as the feel change is not something that the player does not like. If they don’t like the feel, it doesn’t matter what the benefits of the vibration dampening are. Best thing you can do is to try one in a club to see if it works for you. The inserts can be an inexpensive way to make a noticeable difference in how your clubs feel and how your joints feel after playing or practicing.