Are there home-brew photometers for amateur observing of variable stars and are they widely used?
It should be doable with a standard photographic setup, a star catalog with distances and measurements for a some standard stars and a bit of software.

With the usual "ritual" for obtaining images from the sky with a given setup, chip and temperature (obtain dark frames, flat field frames and ground noise frames for division and subtraction) one can calibrate the brightness of an area (subframe around a star) in a photography by comparing it to known stars. The capture software or one of the many post processing packages for amateur astronomy can calculate the brightness of a region, if it is not totally saturated, i would guess if it is well away from any saturation.

A more detailed description: http://www.bellatrixobservatory.org/cvaaI/17/

Edit: An add-on script for one of the amateur software packages for doing photometry: https://pixinsight.com/doc/scripts/AperturePhotometry/AperturePhotometry.html.