Speedy Jim writes:
If there are a lot of them to cut, one way is to
use a circ saw with a masonry (abrasive or diamond)
blade. You can mount a wooden guide strip to keep
the cut straight.

My main concern is precision and neatness of the cut rather than the
time it takes.

If so, would it be better to use a Dremel (with tile cutting bit) or
Circ saw (with masonry blade)?
(Assume in both cases I am using an edge guide to make the cut straight.)