I used the spin stick for agitation for many years and didn't experience uneven developement so I'm not convinced that that's the case... however, I changed to inversion after reading so many people suggesting it. Call it peer pressure :)(posted 8658 days ago)I mix 300ml of developer for one spiral, which is a little more than required, but makes the maths for dilution easy (sometimes). I can't remember the last time I did two films at once. I also only ever have one spiral in the tank although it's regularly recommended to put both in to ensure the bottom one (in the liquid) doesn't move up (and out of the liquid) during inversions. My tanks nearly 20 years old and the spirals never move on the central column. I do this because I may want to use the other spiral to develop a different film type straight after the 1st one, so the spiral is bone dry and the film loads without a problem.
Using the same tank, this is what I do...
Straight after pouring the developer in, I give it a couple of twists back and forward with the 'spin stick' (not sure why I persist with this) then wack the lid on and give it quite a firm shaking, then rap the side of the tank several times. Each minute I give 3 inversions and a more gentle rap on the side of the tank. Negs look fine, just the subjects I need to work on :)