Correct. You leave he spindle off, and the bit just drags along and scratches the surface. I bought this bit on eBay in November 2015, and I can't find the exact one. But here is the description from my purchase history -
1/4" DIAMOND SPRING LOADED DRAG ENGRAVING TOOL WITH 90 DEGREE TIP
Here is a link to the seller. He has 4 different sizes, and it looks like his prices have remained pretty much the same.
Here is a link to what I think is the same or similar -
His description and the pictures are a little odd. I don't know why the picure shows 45/90 and 60/120. But further down it does say that this one is a 90 degree.
This is my first time using the tool, and I had good results, but I am not in a position to recommend this bit or seller.