Avian Biotech is pretty reliable, I've used them many times as well...Just make sure that you pluck fresh feathers out of your bird's chest, and that you send a few and not just one.
Feather DNA-testing is extremely reliable, but you have to make sure that you send fresh feathers that were just plucked, and you send more than one to them, because what happens is if you only send one feather it may not have any genetic material on it to properly test (just like pulling a person's hair to DNA-test or Drug-test, etc., but without the root attached)...If it's not freshly-plucked there won't be any material to properly test, and if you only send one freshly-plucked feather and it doesn't have any genetic-material attached and they test it, depending on what method they use to actually process the test after the PCR is run, sometimes they actually ALL come back as female, because all mammals are female to start out, and they only turn into males when the Y-chromosome is added. I have actually done human sex-testing using gel-electrophoresis/PCR in college/grad school labs, and we tested ourselves, and some males came back as being female on the computer system they were using to do the control tests, and it's just because they didn't have a full root on the hair that they pulled...
Otherwise, hair/fur/feather DNA-testing is just as reliable as blood DNA-testing is, they use exactly the same test that they use on the hair/fur/feather test, it's just the preparation of the sample that differs, and in blood you're always going to have the correct genetic material you need to be accurate. But if you pluck fresh feathers and send 3-4 of them, the test will be accurate.