I'd recommend trying it first if you're interested in it as they do have a free demo you can download to try out if you like. The download link is on their products page:
Even though it exports to Sibelius, here's how you can make it work with Finale that you might be able to try with the demo version first:
1) Scan the score with your scanning software and save it as a pdf file.
2) When you scan it, I've found the settings for sheet music work best if you scan it in 8 bit greyscale and 300-400 dpi. Scanning in plain black & white is usually a disaster. Greyscale is the way to go. If your scanner cannot scan in greyscale, then scan in color if you have to. It'll still work. The file will just be a lot larger.
3) After you create the pdf file, open it with PhotoScore and click on the READ button for PhotoScore to do music OCR on the file. (Optical Character Recognition)
4) There are almost always a few errors the need to be cleaned up. If you get a lot of errors, then it's not worth going any further in my opinion and is more trouble than it's worth. A few errors can be cleaned up in PhotoScore easily.
5) After fixing all errors, save the file as a Music XML file. Finale can open this type of open source music file and you should be able to extract the parts like you normally would from a score in Finale. After you open the music XML file in Finale, export it or save it as a Finale file and you should be good to go.
Again, I highly recommend trying the free demo version first before spending anything on this application. This entire process I've outlined here can sometimes work superbly but it can sometimes be a disaster due to a lot of variables.
Try it before you buy it.