Feels solid, only on a G36C at the moment.
They have a bit of heft to them,feels much heavier than the 320 I have for my L85A3 but it's a more modern design, more to do with the attached handguards probably.
I have a G36K set up as an MG36 with a bipod, I'll pop the ugl on it to see how it looks but prefer it as an MG36.