There are a few chinees clones of the original. And a Polish clone, but that one stopped selling after tons of complains about quality.
And then there are the stolen UM2s. A few have been recovered, but not all of them. As some of these machines where unfinished, they will lack quality control.
I have not seen UM2 clones yet.
In general, we do not seem to mind about clones, as long as they do not use Ultimaker branding.