Tens units are great, they’re just something where I’d recommend doing actual safety research before using. They’re pretty safe, but pretty safe isn’t very safe and in the off chance if something goes wrong it’s unlikely to go only kinda wrong. Electricity is like fire play in that way. Body contact cables can often simulate a tens unit ok, but that includes in risks.

Violet wands aren’t great for a zap feeling as it’s more buzzy. But they’re idiot resistant (nothing in kink is idiot proof) and good for new people for that reason in particular. Cattle prods are mostly safe for people who can handle estim from what I recall though and may be good for that scene in particular. It’s a nice zap with low effort on the dominant side.

That said what you’re saying you want to work up to may be served well by a variable intensity shock collar. Once again, do further research, in general assume anyone talking about bdsm on the internet is an inexperienced jackass with a death wish who learned everything from porn written by someone else who’s never done it. Also don’t put shock collars on people’s necks or do estim on the face, it’s hot af I know, but there’s a risk of palsy.