I used them occassionally in Australia for work without other choices at that time (eg BNE-DRW, BNK-MEL, MEL-OOL), and a couple of times during sales for leisure.
Also I have flown Jetstar Asia several times, to HCM City and Phnom Penh and have some more bookings later to Jakarta and Hongkong ($100 AUD return SIN-HKG-SIN, or actually I paid $125 for the return flight - with an exit row on one of the two sectors.. .not going to complain).
So I do use them opportunistically, when the fares are good, when I only have hand luggae and/or I have a simple non time critical itinerary.
I am more inclined to use Jetstar Asia than Jetstar (Australia) because they are a new carrier on their routes. Whereas I am more principled against Jetstar in Aus, because of the Jetstar-isation of QF routes

Also in Australia, usually you can either find QF to nearby ports for not much more than Jetstar, or at the very least DJ ... out of SIngapore, SQ usually are more than double the price of Jetstar Asia (and other LCC's) and thats usually fares that don't accrue points.
As long as they maintain high safety standards, that is the main thing. In the grand scheme of things, everything else is immaterial.