I wouldn't experiment with any other pesticides to find out if they are safe - they are all meant to poison. A little bit too much or the wrong product - and you will kill your birds. I have no qualms about the Sevin Dust because I have used it for years on our chickens to control poultry mites, we used it on our horses to control lice, and now more recently the pigeons, and I've never had a single instance of poisoning.
I know your question on spot on's is directed to Jay - but I must say this - I won't use them on any of my animals.
Several years ago I had a female cat with two older kittens. I had always used spot on treatments without any trouble. But this particular time, with the cats having a "family unit" so to speak - they reacted by grooming the product off of one another while I was not around. It was a nightmare as I arrived home to all three cats in seizures. All phone calls to veterinarians gave me little hope - I was told if the cats were already seizing pumping their stomachs would do no good, and they would most likely die, there was nothing they could do for me that I wasn't already doing.
The seizures went on for about 12 hours...all I could do was hold them down (they were seizing so hard they would have injured themselves if allowed to). All three cats pulled through and made a full recovery eventually, but days afterward neurological symptoms persisted, eyes that wouldn't dilate, and loss of motor control in their limbs, one would pan her head from side to side repeatedly for hours at a time.
I got very lucky, many have not been.
These spot on products are being revamped right now - pushing for them to make more dosages - instead of the very basic small-medium-large packages they have always made.
But as in my case - even the correct dosage can poison your pet if ingested, particularly at risk if you have multiple animals in one house hold that may engage in mutual grooming of one another.
Now in a loft situation - even if you manage to not overdose them, they are going to preen one another - and they most certainly will not survive.