I would say it's SAFE to snort, as it's not going to kill you, but I don't really recommend it. Snorting all those binders isn't a very good thing, and it will decrease the duration of effects but onset will be quicker.
If you really want the best ROA without using a needle, plugging is your best bet. It offers increased onset, and the highest BA without IVing.
I tried finding info on oral BA vs insufflated BA, but as always I see a lot of different numbers. I think with amphetamines, insufflating typically has a higher BA, but oral lasts much longer. You can always increase the amount of drug absorbed when you take it orally by lowering the pH level of your stomach.
3.3mg is a pretty low dose though. I say start with 5mg if you must snort it. What exactly is your purpose for taking the dextroamphetamine ?