Yuck! Yet more subscription software. Well, maybe it's cheaper than a Parallels 12 upgrade if all you need are the tools. No mention of which versions, besides Parallels 12, these tools work with. I actually use Parallels 11—in OS X 10.9.5 Mavericks. So I cannot use them in any case unless I upgrade OS X.
Or maybe these tools aren't for a VM at all, but are an independent product for the Mac. Not what I'd expect, but, hey, YMMV. And given the number of tools involved, maybe the subscription is a way to keep the price down, or to obscure the ongoing cost of ownership. Hard to say. I just have an aversion to subscription software. Then again, I'm a longtime Mac user so I already have apps to do almost everything Parallels Tools can do. However, if you haven't acquired a similar collection, perhaps these will appeal to you.
Maybe my confusion about the tools derives from the fact that they are included with a Parallels 12 upgrade, which makes the upgrade a good deal if you need the tools as well. In addition, compared to the cost of all the other apps I use, the price of the tools is great, if you don't already have a big investment in comparable apps. Color me on the fence.