Souix me, I love it
Technically, you don't even "need" an air drill. A guy in my local EAA group has built two RVs, still doesn't own an air drill.
That being said, they sure air nice. Biggest advantages are weight, speed, and size. My advice is:
#1 Decide "Go" or "No Go" on air drill.
#2 If "Go", get a good one, and get it new from a reputable dealer. IF there are any problems, you'll be glad you did.
I got the RV kit from Avery and added a pneumatic squeezer. That kit comes with the Souix, and I love it. It is my favorite drill, hands down. That Pneumatic squeezer is the single most expensive tool I have, and I'd buy it again in a heartbeat.
For me, it came down this. I'm building a metal contraption that will cost me well over $30k and will hurtle my body through the atmosphere 200mph at 10,000'+. Do I want cheap tools, or do I want good tools?
Overall, I spent about $3k on tools, including the compressor. That's less than 10% of the total cost of this plane. And I use these tools for a LOT more than just airplane building. In hindsight, it's some of the best money I've ever spent.
Tools are NOT the place to skimp. Pay for quality and service, you'll be glad you did.