I suppose one advantage of the RFM69, versus some of the dedicated temp chips, is that "It takes less than 100 microseconds for the RFM69W to evaluate the temperature (from setting TempMeasStart to 1 to
TempMeasRunning reset). "
A DS18B20 requires a minimum of 3v, which is bad news if it's everything is running direct from just 2x AA's.
An Si7053 only requires 1.9v, but it can take up to 80ms just to power up, plus another 10.8ms before it can produce a temperature reading. It's $2.
The STSC1 is fairly quick: it can power-up and take a measurement all within 1ms, and it's accurate to within 0.3C, but it's $4.23 each and has a very narrow operating voltage range of 1.62-1.98v, so I guess it might require it's own LDO to power it.
For nearly the same price, there's the TSYS02P, which is insanely accurate to within 0.2C, and a resolution to 0.01C, and has a better operating voltage range of 1.5-3.6v. However, it can take up to 150ms to reach an idle state after power up. I suppose it would be a good reference standard for calibrating other sensors.
I suppose the figure of merit will be total system amps per temperature measurement, because impact on battery life will be a significant consideration to weigh in the trade-offs.