I always recommend using a capper to place caps... & thats how I do it - unless an emergency (lost or forgot the capper).
I have roughly one each of every type of brass capper most have handled, and probably the one type that most haven't.
I prefer my straight-line cappers over the snail type. They're a bit faster to manipulate, seat the caps firmer (I don't use a separate "seater"), and are less likely to eject a cap (I don't like shootin em out on the ground). Also, If I was to lose or accidentally dump the snail model I stand to lose enough caps that I may not be able to finish a match, or maybe lose my hair, like cousin G.A.C. & his pals. I like my cap guns to go bang all the time, & there are more factors at play in this ignition system than a cartridge gun, so I don't expect or want the light hit as one can get with a cartridge gun. But, that's just me.
All that, even though I strive to have a spare revolver, spare parts, tools & spare caps in my truck. Hope I don't need it because it only takes one flub to blow the clean match.
If you're capping a cold gun, the cap won't go off on ya anyway. Pressure doesn't set off these things anyway, certainly not the force combined with the softness of your finger. Impact energy is needed or heat/friction. If you don't think thats true, just place caps (only - no charge) on your nipples, then use your wooden dowel, or better a brass or steel pin punch & press as hard as you can. Use a drill press (not rotating - that will cause friction = heat = "bang") or an arbor press. After all that excessive pressing, you may find the cap is now a dud if you drop the hammer on it.
In summary, it makes no sense to cap individually using your fingers...unless you have to. And, if you do, be sure it's a cold gun. Do you really want to spill caps that cost 2-3 times the cost of a primer? I certainly don't (Mr. Cheapskate)...In fact I can load a .38 special with that other "propellant" for less than the cost of a cap (@ retail price).
As far as pinching caps....it actually works in a "pinch"...but the way to pinch them is not intuitive. If I never get round to writin' my book, I'll have to put it in a u-tube..
The reason caps go sideways in the Cash snail capper is due to the height of the caps. It is possible to tweak the capper with a mallet.
BTW, Ted Cash isn't making cappers anymore (he sold the business).
Slim