I don't use them but I've seen pictures of coins that were cleaned with them. It seems to me that they are very abrasive but if the coin isn't valuable I see no harm in using them.
I've had a set for a year or so. You might be able to effectively use them with a light touch and practice, but I've only ever used them to "brute strength" a date off of a coin or similar. Seems like I paid around $20 or so for the 4 pencils in a round plastic sleeve. I would encourage anybody to get a set, for those times you need a precise scraping instrument.
I have probably used the steel wool pencil the most...it can make an iffy date on a cent come right through the grime.
They work well. As diggin' said, don't use them on any find with significant value because there is a level of abrasiveness.
With the 4 pencil set, the ones I use the most have the sharpened pencil ends as opposed to the steel wool and scalpel ones. They work excellent for bringing out dates or lettering. Be extra careful if you using the scalpel one, it will scratch very easily.
Take your time when using them. Common date corroded old wheaties work well to practice on.
I've used them with varying success. They work really well on Wheaties and Indians. They also are pretty good at taking off the grime on older nickels. The only thing I regret using them on was a King George II halfpenny. It was already really corroded but that removed any remaining details.
Nothing wrong with that method if you like the way they look, Chip.
But I can tell you that anyone who has any numismatic instincts is going to prefer the before pictures of your silver coins to the baking soda rubbed ones. I would keep that in mind for any silver that has more than bullion value.
That 1923 Mercury dime is not a rare date by any means, but as an earlier date merc it does have a bit more than bullion value. You brought down the value (albeit minimally) by doing that abrasive cleaning on it.