I have had many good experiences with their products. However, I have also run into some oddities with their springs not matching the factory specifications in annoying ways.
First example is, their "factory standard" recoil spring for the Browning Hi Power is in fact quite a bit longer and heavier than the factory standard recoil spring that FN/Browning actually produces. This can make a Hi Power (already hard to rack the slide) become actually impossible for people with below average hand strength to rack the slide, at least with the hammer down. Whereas, to contrast, putting a new Browning spring in, racking the slide becomes much easier for the same person who had trouble racking with the Wolff spring. The issue remains long after break in, and I've totally given up on their springs for this model of handgun. I'm skeptical that every gun benefits from "extra power" recoil springs.
Some of their springs for older pistols can have spotty fitment. This probably has more to do with variation in the original construction process of the guns and not of Wolff's springs, but with my FN 1910, the slide just binds up if I try to use a Wolff recoil spring. On the other hand, I can buy an unbranded, used FN 1910 recoil spring from Numrich (presumably from a random, original pistol) and it fits in the gun every time. Another example is I once got a Wolff magazine spring for a CZ 52 magazine that had a weakened spring. The Wolff product appeared to be a scale model of a real CZ 52 magazine spring, quite a bit shorter and thinner than the 62 year old original part. I have no idea what they were thinking when they packaged that thing up, but it didn't feed correctly, much less hold the slide back.
Keep in mind, I've had many good experiences with their springs, but I hesitate to say that all their products are "good to go." Buy one, try it, and if it works, then use it.
