640 units are better than 384 units, but the 384 units generally work well at reasonable ranges. Nothing under 384 is worth buying so don’t waste your money. AGM, Pulsar, Bering Optics, IRay/InfRay all generally do a good job, but there are also others trying hard. Take a look at the reviews on the Late Night Vision Show YouTube channel, or Hans East Texas channel. They are long winded and unnecessarily stretch their material, but are truthful and immensely experienced. I recently bought the Athlon 640 unit because it was a great deal but the company has a good reputation for warranty service which is an important consideration. My scanner is a Bering Optics model, but, again, I’m also happy with my Pulsar 384 riflescope, and my old AGM clip on was great.