Preface
After learning freestyle, my Xiaomi band gloriously malfunctioned after only 8 uses.

Options
So I started looking for reliable alternatives on JD and Taobao:
- Moov Now Swimming Smart Band: ¥399.00
- Swimovate PoolMate2 Standard Edition: ¥790.00
- Swimovate PoolMate Live Agile Edition + Swimovate PoolMate Live Agile Edition USB Data Clip: ¥945.00 + ¥335.00
- GARMIN Forerunner735: ¥2280.00
- COUNTU 2018: ¥288.17
- SportCount: ¥238.00
The final choice, as the title suggests, was COUNTU 2018

Reasoning
Moov Now was my first choice, but after reading several reviews, I found its measurement accuracy was still mediocre. Having learned from the Mi band experience, I passed on it.
The two Swimovate models are listed separately because of price and features. In theory, these two watches achieve professional-level measurement accuracy. The Live version has an additional data export feature, but requires buying a USB data clip. If only considering measurement accuracy, buying the Swimovate PoolMate2 Standard Edition is sufficient. Pending.
GARMIN Forerunner735 is a professional triathlon watch, but the price isn’t pretty, so I passed.
Two remaining options are non-band form factors: COUNTU and SportCount. These are actually the only two finger-ring type counters for swimming that can be purchased online. The SportCount’s operation and display are reportedly quite dumb, while COUNTU as a domestic brand has made many user-friendly optimizations.
In the end, I chose the more hardcore and cheaper option between Swimovate and COUNTU: COUNTU.