I don't own the UD100 but from what I've gathered so far; it's an average bike.
Not as remarkable as the YBR, but neither as terrible as the Ravi Storm 125.
In fact, here in Lahore, a lot of چنگچی رکشے use UD100s and other similar Chinese 100cc motorcycles so they 'must' be quite durable, I'd say. But with that being said;
Buy at your own risk!
Because like I mentioned earlier; I've no personal experience with UD100; or any other Chinese 100cc motorcycle for that matter.
Hope it helps.