Great multiperformance shoes!
The Salomon S/Lab Pulsar 4 is a great offering for multiple distances. Although, while on paper it still carries the S/Lab sticker, it has become very "civilized" now and less of what we used to know from an S/Lab offering.
Fits true-to-size, by toe box is much wider than in the Pulsar 2 and 3. The shoe is also less nimble than its predecessors, making it less technical trails oriented (although it still is better than its direct competitors).
Outsole grip is satisfying in all terrains but the muddiest ones. The lateral support is welcome, making this shoe fairly stable. The "garage" for the lace is much easier to use than with previous Salomons. The midsole is pleasant, a good blend of softness and firmness when needed: not too bouncy but not too firm either. As i said, "civilized".
While a great shoe, it does not replace the Pulsar 2 or pulsar 3. I'd say it complements them rather than replace them. If you race technical terrains up to 1/2 marathon, go with the Pulsar 3. For a bit less technical terrains (although a very capable shoe) and longer distances, go with the Pulsar 4.
Direct competitor: the Nnormal Kjerag 02. This shoe offers the same ride characteristics, although a much (too much?) wider toe box, a lighter weight (although not much difference on foot) and a bouncier midsole. But it is less stable and less nimble on technical terrains with more chances to twist ankles. Price is cheaper though. I personally use the Kjerag 02 for training sessions on less…