I'm about to shine one on a coin for the first time. In practice, they're quite similar to the MR16 halogens I normally use, which are mounted on gooseneck track fittings and deploy from above rather than below. One of the main things I actually expect to gain is a lessening of the ambient temperature around my photography - the halogens used to get dimmed down after each image if I was moving the coin, just so my lens hood wouldn't melt.

I'm going to lose in terms of exposure, because these are not nearly as bright as the halogens. I suspect this might actually become a factor with duller coins, as there are times I'm already down to 1/15 with 100 watts of halogen beating down on the coin. There will be times when the halogens will be favored over the LED's; this will be reflected in my final lighting setup.
The basic technique hasn't changed. It's still either "one at 2:00" or "two at 10 and 2," with the final angle determined by the relative luminosity of the coin, according to the paradigm by which we've been taught constitutes a "good coin picture."
However, the Jansjo's offer a
huge potential over the halogens in that they can easily be used with tweaks such as Ray's Super Diffuser design, which has thrown me into a whole 'nuther frame of mind about how to shoot truly lustrous stuff. I'm going to move for a bit towards longer exposures under lesser lighting, maybe with some directed diffusion (think about that term without your brain hurting

). It might be possible to somewhat tweak that paradigm we've been living under.
It's gonna be a long winter. I have a lot to play with, and these Jansjo's are but one player in the game. The first foray will be more in the P&S direction; I've a new one which seems to rather enjoy shooting coins. Mind you, this was hastily set up (with two Jansjos), no Custom White Balance, handheld, and downsized to post here:

That was the 8th image I've shot with the camera, and the very first on the Macro setting. I'm amazed that it was able to do this at 1/160 in Aperture Priority, and stabilize the image with my moving-target hands. It's a heck of a little piece, my first non-Canon camera with this kind of promise, and worth finding out what it can actually do.
What camera? Heh. Either extract the EXIF data (it's still there), or wait for the thread.
The best thing about a bicycle is that it uses no gasoline, therefore the chance of fiery death is greatly reduced.
First Catman, then Gary Burke and now Bigg Fredd - there's one heck of a coin club in Heaven.