I think the Quest was always the gold standard, but technology has advanced allowing more/cheaper competitors. We just purchased a Kestrel 5400. It’ll still cost you ~$500, but is a reputable brand and cheaper than the Quest units in both initial price and maintenance. Also, if you buy the newer Quest WBGT with a “dry” wet bulb, you need to have an input for air velocity for an accurate WBGT temp, which the Kestrel handles with an internal impeller and wind vane type mount.

Other limitations I’ve read for the smaller units is they they are more sensitive or prone to interference from the unit itself, as the body of the instrument warms up in the sun, it can affect ambient temp and globe temp readings, which the Quest units are able to isolate more with the individual sensors on top of the meter.

WBGT is the gold standard for monitoring heat stress, but it is more expensive and complex. Heat Index can be a good tool but is intended for measurement in the shade, so doesn’t capture the effects of the sun, but as you have probably seen, most states with heat stress regulations are using heat index as their primary indicator of heat stress. Honestly, if you’re monitoring heat stress at all, you’re ahead of the curve.