You get what you pay far.

The lower the dollar cost the less consistent and finicky they are, especially those that rely on sunlight. Speed changes as light angle or intensity changes.

I own a CED which has worked reasonably well and provide pretty consistent reading without regard to lighting conditions.
Good enough for most data collection purposes.

I also have a Kurzzeit BMC-19 and BMC-21 which are great.
The new BMC-19 is wireless to my laptop which is a joy. They are supposed to making the hooks for pulling the data directly in to Quick Loads for us internal ballistic geeks.

Have used or shoot over most the other and I would only recommend the Oehler out side those I own, it is also an excellent product.

If you are a geek the Kurzzeit BMC-19 is the ultimate.

As a side note, use a rest when shooting over your chrono, it not uncommon to get one shot, please don't ask.

Good Luck and be safe
Ruggy