I've used many different 'devices', from laser-emitting fake-cartridges, laser-emitting bore-inserts, and even 'Convet-a-Pell' in a Contender (which I guess isn't 'dry-firing', but reduces the power enough for indoor practice, to the one I settled on for the past 6-8 years. The 'Mantis'.
I upgraded to their newer model last year, and it is nice. They can work on handguns, rifles, shotguns, and BOWS, with both 'dry' and 'live' fire.
They interface with your smartphone so you get a multifunction shot-timer, and target analysis that tracks the most MINUTE muzzle movements just before, during, and after the hammer-fall.
It thus enables great analytics to see what you are doing wrong (I had quite the list...
Normally I dislike doing anything 'electronically' that I can do on paper, but it does make practice fun and efficient.
Anyway, it is worth checking out, and I wonder if any of you guys use some other similar thing.