I have a brand new in box 3/8" ROH diamond stone by Pro-Filer (I bought an extra one some time ago, then changed my ROH, so never needed it). This is a hand-held sharpening tool that has been amply discussed on these forums. If you are not familiar with it - you can see thread here: https://skatingforums.com/index.php?topic=6837.0
Note: This is the stone ONLY, no holder/chassis, no tape, no side stone, etc. Best if you already have a setup and just want a new stone. More on their website here: http://www.pro-filer.com/profiler/
$40 includes shipping by priority mail to US
Perhaps you should mention that from the manufacturer (Edge Specialties), the price is $45 + $16(shipping) =$61. And that probably isn't priority mail, so it might take a few weeks.
So your price is a good deal. If I needed another diamond stone, I'd buy it.