Like I say, they are fierce. Approach with caution. I use a flap wheel to shift rust usually.Needle gun looks like it would go right through the chassis !
Horses for courses really. It depends on how bad the rust is as to what device you use. Personally I tend to use either a wire wheel, a flap disc or a clog-free disc, I also like a phosphoric acid based rust converter to slap on, it helps stop the rust in its tracks. I don’t have an air compressor, but needle guns are good for really heavy rust, by which point you may be needing a welder!
I find flap discs tend to polish the rust, an angle grinder with one of them wicked wire bush attachments is bloody good, decent gloves and face covering essential.
Bottom left and top right versions are fast and evil!
+1 on the protective gear if you use these, I did when I stripped my chassis, thought I was alright with gloves and one of those full face masks that are used when heavy duty strimming. Had a sharp pain in my leg and one of the wires had come off and went through a pair of overalls and a pair of jeans to stick in my leg, not impressed. May be safer if used in a drill (corded), angle grinders are rather quick.
If a needle gun goes through the chassis, it needs welding then !!
Spend 30 odd quid and buy a mains grinder as a battery one isn’t great to power a wire cup brush, which is the best thing for scale and surface rust removal IMO.
Or remove surface rust and paint the chassis in old engine oil at least twice, do it every couple of years and let the dust etc mix with the oil to make a coating of thick mucky oil and it'll last forever