I'm not intending to download the app. My essential reasoning is that it's virtually irrelevant to my life style.
1. It would be extremely rare for me to spend 15 minutes within 1.5 m of anyone without either knowing who they are or, alternatively being on a plane when my Bluetooth is off.
2. I'm dubious of the technology used. I've worked quite a bit with Bluetooth and that 1.5 m has to have a huge error factor.
3. I'm dubious of the logic used. Thirty seconds near someone sneezing would be enough for infection to happen.
4. Potential for false positives. I see the point in high density situations, where the general vague nature of the information may be of benefit but in an Australia, already practising social distancing? I do not want to be logged as a potential positive, based on a phone app. A phone is not a scientific instrument. One little quirk and perhaps that 15 minutes turns to 15 ms? Perhaps the 1.5 m doesn't work as described on the packet and logs anything within range, which can be 100m + on a good day (50m on an average day!).
5. Potential complications. I use the Bluetooth on my phone quite extensively. I don't want some unknown app messing about with it.
6. Battery life. Bluetooth is a wireless transceiver. To work, it needs to be on. In this context, to work effectively, it needs to be both transmitting to say it's there and also receiving from other phones saying that they are there. If it's really smart and sends out low power pulses every 7.5 minutes, the transmission side could be reduced but the receiver has to be constantly listening.
7. It's dependent on all parties having Bluetooth turned on (refer #6 above!). If half the population downloads it but only turn their Bluetooth on when they feel there's a risk, most of the relevance evaporates.
Basically, I can see no personal or social benefit to be derived from my installing this app but I can see plenty of negatives. Battery life alone is sufficient for me to lose interest.