They're handy, for sure. I have them in Coarse and Fine. Even at their more typical street prices, they're still a good deal and won't break the budget. Think I might've paid somewhere around $10 or so, for each of mine. My only issue with them is, the plastic swivel/ring assembly from which they hang can be prone to breaking; I've broken one of mine. If DMT could make that a bit more robust, it'd be essentially perfect in my uses.
Both Victorinox and Opinel (their stainless, especially) respond very well to a wide variety of sharpening media and grit choice, from natural stones all the way to diamond. So with a light touch, even the coarse diamond from DMT specifically can work well. I've tinkered with Coarse, Fine and EF DMTs on a couple of Victornox paring knives I have, trying to decide which edge finish I like the most. They all work well with this steel, with an absolute minimum of passes and the lightest pressure used. I usually settle into the 'Fine' diamond most often for it; but I can see why some might prefer something a little coarser, again used with a very, very light touch.