Ive had a UGB for about 6 months and about 2500 rounds through it and have never had a problem. Seems like shooters either love them or hate them. I absolutely love mine. I can't compare the weight since I've never held the Ljutic, but the UGB doesn't seem heavy to me.
I have both. I bought a UGB new and I have a very old Ljutic mono. They are both heavy guns in my opinion. I think that the UGB is just a little lighter. The UGB is a very balanced gun. I will tell you that if you are going to buy a UGB look around. I paid way in excess of $3K for mine. I saw one sell on this site a couple of weeks ago for $1600 and that was the trap version. I have about 1500 rounds through my UGB without a single problem. I have several guns and I might consider parting with the UGB for the right price. PM me if interested.