I use the 150 gr version in 308 win. I shot two roe deer in the last few months. Both were hit behind the shoulder and both ran or better said stumbled only a few meters before collapsing. Massive blood loss and the damage was also quite massive considering it's a monolithic bullet. They are very effective bullets. I'd say they are somewhat similar in performance to Barnes TTSX but they open up to a form of a mushroom. And they also cost less. They are not made from pure copper, they are softer a bit and as a result they do not foul the barrel as much and you can most probably also achieve higher velocities safer as there is less pressure in the barrel. But on the other hand the bullet could lose the cutting petals in a case of extremely deep penetration. But even if they lose all of the petals, they still penetrate as a FMJ. Most of the Slovenian hunters that use them are pleased by the performance of the bullets. Slovenian manufacturers currently also produce two other types of monolithic bullets, they are called LOS bullets and OK bullets. Both are also very effective bullets, but they perform in a different manner as the front part fragments upon impact.
Hirtenberger ABC was also a monolithic bullet, which was invented some 40 years ago by a Slovenian engineer Avčin. He sold the patent rights to Hirtenberger and Hirtenberger then loaded the ABC bullet until the company was taken up by RUAG in the 2000's. A lot of Slovenian hunters still think it was the best bullet in serial production ever made. I think ABC was also the first monolithic bullet in large scale serial production in Europe (or at the very least one of the first). So there is strong tradition of making monolithic bullets in Slovenia. The outer form of Fox bullet looks quite a lot like ABC bullets, although the performance is different, as the ABC opened up to four cutting petals and the FOX opens up to a form of a mushroom.