Yeah, you can even donate appreciated shares through them! If I had known ahead of time about this match, I would have tried that approach.

Edit 4/8: I called CVS and confirmed that they are not using "live or work in the county" as a restriction.

Per https://www.vaccinateca.com/, many of the rural counties within a few hours drive of the Bay restrict vaccines to people who live or work in the county.

Sacramento:

Eligibility: Sacramento County residents who are 65+, as well as people who live or work in Sacramento County

Fresno:

County restrictions: Must be a Fresno county resident or work in Fresno county

Placer:

County restrictions:  The Placer County Public Health Division is currently conducting vaccine clinics for people who live OR work in Placer County.

Kern:

County restrictions: Must be a Kern county resident or work in Kern county

Madera:

County restrictions: Must be a Madera county resident or work in Madera county

Sounds like a fun project, but I'm skeptical that this would be widely used.

As a user of the tool, would I be able to see how much had been donated to each candidate? If I support candidate X and I learn or infer that very few candidate Y supporters have donated, then I would have a high expectation that my money would go to candidate X rather than charity. The gamification effect of trying to out-donate my opponent would be weaker.

I think there is a high possibility that the tool would primarily attract the attention of left-leaning people. One reason for this is that the alleged advantage better funding affords to campaigns tends to be a left-wing talking point.  And of course, most of the rationalists and EA-aligned people I know lean left.

Also, I'm probably not the target audience because I never donated to a political campaign. But my intuition is that I'd get fuzzies by knowing my money went to my candidate. Will partisan donors get fuzzies knowing that they stopped money from going to their less preferred candidate?

Finally, I agree with Linch that the tool will best serve donors who think the difference between how the two campaigns use the money is in expectation neutral. Unfortunately, I worry that the mental burden of having to even make such an evaluation -- the marginal value of one's dollar to each candidate's campaign -- could deter non-EA people.