As topic: Does anybody use it and is it usefull against improved monsters?

Regards

Looking at what it does in NI I don't see why it wouldn't be useful, although I don't recall trying it - each blast deals 2d10 crushing damage with a save for half, which bypasses magic resistance. I believe this would be effective against most IA enemies, although it will not deal much damage. It also causes Stun and a Wing Buffet effect, although if you save against the damage you don't suffer the Stun. Of course some enemies will have immunity to Stun and/or Wing Buffet, so wouldn't be affected.

The problem is that (as far as I know) the Horn also affects party members, who would be vulnerable to the Wing Buffet and damage even if somehow protected from the Stun. So probably it's best used only in desperate circumstances. Maybe it could be useful for interrupting enemy spellcasting if you suspect a dangerous spell is being cast? Try it and let us know.

Cool! Yes in some desperate situations it could possibly be worth carrying around. And crushing damage isn't that bad in IA AFAIK I'll save it then

As I said, I haven't actually experimented with the Horn. Near Infinity is pretty reliable but it'd be best to try the Horn out in your own game on some unimportant enemies before risking it in an important battle.

as I used it really rare. but as i remember it doesnt effect party members(or maybe it is because i use it only when i am soloing with my vagrant and other characters are standing behind)

I used it. It affects party members, so you should use it only if party members are farer from user. Damage is very small, but it can be used in cramped situation and it can give you a free round.