My take home is to not to use chalk for raising alkalinity if baking soda will work acceptably, e.g., does not raise sodium excessively. My reasoning is that the calculation for the contribution to alkalinity from chalk is a crude empiricism that does not take into account a specific users chalk source,equipment, and procedures that could lead to different amounts of chalk being dissolved over the length of the mash.
The problem with chalk is that it appears as though you can't predict the alkalinity it will contribute to the mash. It is notable that you can't predict the mash pH very well regardless.
If you use a pH meter at dough-in, using chalk to raise the pH if needed works just fine as you are doing it empirically and you aren't adding any unwanted sodium. If you rely on predicting things (you don't have a pH meter), then baking soda will be more predictable subject to the caveat about too much sodium.
If you aren't worried about working with it, potassium hydroxide would add a predictable amount of alkalinity and no sodium. I use it in mead making and use gloves and eye protection to mix a solution of known strength (whatever it is that the SPHBC folks recommend) and then gloves only when working with the solution. Never broke it out for a mash as:
1. I rarely measure a mash pH that is lower than I want, and I typically start with modestly negative RA and
2. When I do the amount of chalk required to raise it is uniformly pretty small.