Whenever I've Googled the different Franzis apps, I've found them close to the top rank, but not best in class, FWIW. So if it's something you'll use, IMHO they're generally worth having if the price is right, e.g. as a giveaway, or if the sale price is good enough.
Black & White Projects is designed to turn full color images into black & white. Why? Technically speaking, you'll have all of the data from the full color image, which is more than you'd have if you shot or scanned in B&W or grayscale. And all of that data can be used to get you a fuller range of B&W tones than you'd easily get otherwise. Aesthetically speaking, there's really very little that I can say... you either like what can be done with B&W prints [or images], or you don't.
Black & White Projects 3 will open RAW images, & the software itself is pretty light weight in terms of its impact on Windows. That said, Franzis uses a DRM packager for their setup file, & that setup file includes an older version of the C/C++ runtime files from Microsoft. Besides those runtime files, both 32 & 64 bit versions of the software are included, along with several copies of their P/Shop plugins, many of them appearing to be identical. Those plugins are also available in the "Photoshop Plug-ins" folder when you unzip the GOTD download, I'd guess to let you add them yourself to your other image editing apps.
[For P/Shop CC 2015 I put Franzis plugins in the Franzis program's folder, then put a shortcut to that folder in P/Shop's Plug-ins folder.]
Back to the Black & White Projects 3 installer... I tried to monitor the installation in a win7 32 bit VM, but recorded 60 some thousand new registry entries. It happens... most all of those new entries will not be there after restarting Windows, but it does make it [nearly] impossible to tell what installing B&W Projects does to the registry.
I already had B&W Projects 3 "Elements", which judging by the price on the Franzis web site, is a somewhat cut down version of today's GOTD. The key I already had worked to install the software, but I still needed to sign in & request a new key to actually activate this version [some Franzis apps don't require activation once they're installed, but this one does].
Personally I've played with the different Franzis apps occasionally, but never found anything that's a must have -- that doesn't mean no must have features exist, but only that I've never come across them. I haven't gone out of my way though trying them out. Admittedly my attitude may seem a bit chauvinistic, but I fail to see why if Franzis hopes to sell to native English speakers, they can't invest the time & effort to make their giveaway registrations easy for those people that natively speak English. *To me* the extra DRM says we don't trust you, & the registration process being only in German, says you cheap English & Americans that grab our free stuff will never buy anything anyway, so why should we bother? I also interpret it as a lack of commitment, figuring that if penetrating the English speaking market is a whim, support for the English language could disappear with the next version update. And that in a nutshell is why I didn't buy their denoising app when it was last on sale.