It is unfortunate that you didnt do research on the budgies to find out what there needs are before you killed them, but you learned from your mistake.I personally would be cautious ... I unfortunately managed to kill of 2 budgies with the use of plug in and battery operated air fresheners within 2 months of having them. I have also noticed that my pet rats had suffered with them too ... My previous rats started sneezing and were getting respiratory problems and subsequently died.... but the replacement rats have not died after discontinuing the use of air freshener and have not suffered with any breathing problems. T's have a different way of breathing to mammals but I would still be careful as any chemical in the air ends up settling somewhere on surfaces and walls etc .... and could easily find its way into the enclosures through the ventilation slits/holes/mesh.
We have budgies also and we found out that you can use sage sticks as an air freshener. It doesnt need to burn very long either.
So maybe that is an alternative to commercial air fresheners that you can use around Ts also.