Yes, H&N always look after their customers and they continue to look for ways to improve their products and services as well. I have been using their pellets/slugs for awhile now I have gotten great results in my guns. In particular the 25gr Gen2 slugs in my FX Impact MK2.
Thru my personal experience with lots of testings and finding the right slugs for my Impact, I can tell you that not every gun will shoot well (INITIALLY) with any one particular size, weight and calibre, pellets or slugs. Most people don't realize that their barrels, Reg pressure, Hammer Spring and speed of projectile greatly influence the accuracy of such projectile. There is a "perfect tune" for each projectile that just works, but user have to find that out by playing around with the Reg/HS/Speed.
A small increase or decrease in speed can alter the accuracy of a perfectly tuned gun. I was shooting my FX Impact MK2 with the H&N 25gr Gen2 slugs in size .218 very accurately out to 100 yards at a tuned speed of 984fps during the Summer time. Recently my accuracy was affected by the colder temperature and I lost 15-20 fps. Luckily I was able to make minor adjustment to the valve and I got my accuracy back again even at the new lower speed of 967 fps.
Moral of the story is, don't discard a projectile being no good whether it is pellet or slug before giving them a fair amount of testing time by adjusting your power setup. Once you get the right setup with your gun (harmonic tune) and the projectile, enjoy the fun of hitting the target repeatedly. That is why we enjoy this crazy hobby of air gunning, isn't it?