It would depend on if the user was using alone or with a partner. Alone? I would not recommend it at all because it's simply not safe since it has no flared base. As much as it doesn't seem likely, it can get sucked up and would require medical attention or at least a bit of a hassle to retrieve.
If you have a partner that you trust entirely and whose hand will not leave the toy for so much as a second, it could feasibly be used as a prostate toy. My man I and I haven't tried this one but we did try the marble g-spot slimline early on in exploring his p-spot. It worked alright, but not as well as toys specifically targeted for the p-spot. Plus, as I said before, you can't let go of it at all for safety reasons.