[Quillman]

Cutter (flute) length usually no more that 4x the shank diameter.
And even if that standard is met it doesn't mean the cutter is safe.
Appreciate that these things are only supported on one end.
And, as such, subject to a lot of deflection.
Biggest cutter perhaps this one.

 

[Quillman]

Was a consultant for a major vendor with respect to your first (3" = FL) entry.
Not a pretty sight (the injury). 65,000$ for the ER and subsequent surgeries.
A long skinny bit like that is simply a loose, pit bull terrier.
Not recommended x this user.