My review of the Truthear Hola is up in my HiFiGuides thread.
The Truthear Hola is a solid contender at the sub-$20 price point. I do think there are real gaps between the Hola, the Moondrop Chu, and the 7Hz Zero with respect to various aspects of technical performance. With that said, while these gaps are concrete, they are small enough that your primary decision point should be based on the subtle differences in tuning between the three. For those just entering the IEM space, my recommendation would be to purchase all three to better inform your more expensive purchases down the road.