Hello folks,
I finally bought myself a thumbwriter, and I have a few questions about it. I'm a bit reluctant to just go out and practice it, because the price for messing up this is significantly bigger than messing up e.g. a doublelift.
I want it mainly for guessing a letter of the alphabet on a small paper (similar to bicycle playing card size). Could someone experienced help me out in this?

How do you hide the writer if you want to hand the card face down to the spectator with your left hand? Just underneath index and middle fingers, then slowly lowering the hand, then to the pocket? Or would you be so bold as to hand the card with the same hand?

Or do you ever hand the card to them, maybe you prefer to just turn it around, and hide the gimmick behind pinky and ring finger in flipping motion?

Do you care to stand further from the spectator while writing or it doesn't matter at all? I suppose you cannot be completely surrounded?

Corinda's "13 Steps to Mentalism" has considerable material about the "Swami Gimmick." It's also discussed in volume 4 of the Tarbell Course in Magic. Thomas Baxter probably wrote the definitive work on the tool you mention -- it's a bit pricey but contains everything you ever wanted to know on the subject.

I should also have mentioned Bob Cassidy's "Swami Tech," an extensive treatment published just over a year ago by a luminary of the mentalism world who hangs out here in the Magic Café.

Thx a lot for those recomenndations, I've read something already, but it was mostly about routines. So I would love to know psychological subtleties from someone who used thumbwriter a lot.
I'm mostly concerned about handing the card to someone with the same hand or should I switch hands? I've seen D.Brown switching, which wasn't logical, but he was fluent and natural about it. Second concern is hiding the thumb after writing, and the distance from the spectator.

Corinda's advice, given in all caps, is "FORGET ALL ABOUT IT." He adds, "No one but you is aware that you have something stuck on your thumb." Your audience doesn't know you have a gimmick, and they don't know what you're going to do with the gimmick. We don't go through life staring at each other's thumbs, so if people are burning your hands it's because you yourself have done something to call attention to them. A performer feeling "guilty" about a secret prop or move is always going to call attention to the secret.

Yes, I've seen Richard Osterlind wearing a nailwriter at the start of his show, and just casually walking with it, nailwriter is small and hideable behind one finger, I have a thumbwriter which is quite big.
Personally I prefer to take it out on right hand behind a card, passing the card and thumb to the left, showing right hand empty, get pencil, write behind my back if able, so they don't see the pencil's movement. Thumb is still palmed in the left, then put on, while both hands hold the card for 1 sec

Actually I think I should have written my questions in 'Penny for your thoughts' forum...

Might be a good idea to also post it over there, but Doug´s advice is spot on.

Luckily, I've seen Lior Suchard using a thumwriter on yt, he really did forget about it, weirdly coloured thumb with dark spot on it, it was recorded, in view of spectators, and nobody saw anything. I think I'm overreacting now, and don't need my sneaky moves, nor worries, just script, confidence, misdirection, and showmanship.

There are many different types of swami gimmicks and tricks you can do with them. Try as many as you can, and see which one works the best.