Poor machining, fit issues, inexpensive(soft or fragile) material, too much flex in the wrong places, soft material fasteners, missing parts from new kits, general parts supply from distributors, long shipping times from overseas, no local tech support, ambiguous setups for specialized track locations, infrequent updates and improvements.
This wasn't ALWAYS the case, but more often than not. I like wrenching, but not on the same things over and over.

I don't want to single any one manufacturer out, but for me, it gets the "budget" price for "budget" reasons.
No Thank You.
I take time now to decide what I spend my money on, and the smile on my face is generally proportional at the end of the day.
If budget kits are for you, bravo!
Last word, buyer beware.

....All that being said....I firmly believe that USGT, as well as VTA, were perfect classes for "budget" chassis to be competitive.
They belong on the track with everything else, and are excellent for getting new racers into the groove without heavy cost.