yes, it seems reliable- I used to observe people I spent time with and formulate an idea of what I thought their handwriting should look like- then I would check it. If I was wrong ,I found out what I had missed- after 30 years you get pretty good- as good as the guys at the carnival who guess your age and weight!
For example, I mentioned that depressed people have handwriting that slopes downwards on the paper. think about how a really depressed person feels- they can hardly get out of bed, they have no pep in life- now see how their shoulders droop-arms hang by the side. When they write , this negative energy tends to droop the hands down- causing the handwriting to slope downhill on the paper. Make sense now?
Turn that around and visualize the optimistic- happy ,full of life person- he is in such a hurry and so full of energy that the handwriting is climbing up off the paper- causing the upward line slant of the sentences on the paper!
I don't belive you can get the subtle information that some analysts claim to see, but the important personality traits do come out in your handwriting.