Currently skew transform uses tangent values. I learnt this only from The Skew facility of the Glyph Transformer - #2 by Bhikkhu_Pesala Neither the user interface nor the documentation explains this. (Sorry if I missed out seeing anything.)
Angles are more naturally understandable than tangent values. Inkscape uses angles for the skew transform.
Please change the skew transform tool (whether in Transform toolbox or in Glyph Transformer wizard) to use angles and not tangent values.
Use the italic transformation — then the angle is shown in degrees.
This still doesn’t make the angle capability available from the Transform dialog where it is often likely to be used. (I personally use the Glyph Transformer when unavoidable as in for multiple glyphs etc.)
If the only difference between the italic transform and the skew transform is the input units, then the italic transform should be replaced by the skew transform by changing the input units of skew to angles. Tangents are NOT intuitive.
I agree, and will most likely further enhance the software per your suggestions. They will not be part of version 6 though.