Per-plant yield depends on how large the plant is. IMO, it's better to think of grams per watt, and how many watts per square foot you'll need (and how many plants you can fit into a square foot, or how tall they'll be, which may require additional watts for penetration or side-lighting). 1g per watt is what people strive for, and you need about 35-40w/sq ft of cheap Chinese LED (or, 25w/sq ft of quality LED like A51).
I got 95-100g from a Blackstar UFO running 85w actual. That was approximately 21w/sq ft which was underpowered for the space. Lately I added
4 Cree lightbulbs from Home Depot (<<link) to bring that up to 30w/sq ft. (The Cree light is more in the high-quality category, so I think I'm in the sweet spot now with a combination of quality light and cheap Chinese.). I harvested a few days ago and the buds have been steady at 64% in the jar. They weigh 155g. That's 1.12g per watt. The per-watt yield is about the same, but I got more per square foot by adding more light, and I did it with fewer watts per square foot by using higher-quality light.
If you're starting out, I think you'll be happy with a Chinese import. The downsides are that the spectrum might not be as finally tuned as an Area51. The electrical consumption and heat won't be as good. But, just starting out, I would have been
very pleased with anything near 1g per watt, or 30g per sq. ft. After seeing that, the hook would have been set and I'd be forking money out for more Cree bulbs and/or A51 fixtures.
You just have to be prepared for how they may not last as long, may not produce dense buds, won't have the penetration (you'll need sidelighting, or keep the plants shorter via reduced veg time, scrog, training, etc). You could have a disappointing support experience. From what I hear, Chinese sellers tend to "negotiate" warranty service by playing the angle that you have to mail the fixture back to China. From that starting point they try to get a little money for mailing replacement parts to you. Not a bad deal, but you have to set your expectations accordingly. Even to the point that you may have a disposable light, which isn't the end of the world for $150.
Where I think it doesn't make sense is when someone buys a rebranded Chinese import at a premium for that more on-shore experience. For example, if you'd pay for a Blackstar, you might as well spend the relatively small additional amount for an A51, Onyx, Hans Panel, or Cree lightbulbs. (That's especially true when you get into rebranded imports like HydroGrowLED, BlackDog, GrowBlu which leverage a "secret sauce" hype.).