I've only used it on duck eggs, but think it should work with other eggs too. Didn't have the stethoscope with the quail eggs. One thing to remember is to turn off the incubator and the egg turner (if used) to cut out those noises. Don't forget to turn them back on once done (have done that...
You can see blood vessels as early as day 4. Best is to check on day 7 and from there on every week. You should see blood vessels at day 7, but I usually keep those without any for another week to make sure. I sort the eggs in the incubator accordingly. If they are clear at week 2 they will...