Maybe get the free one first and see if it’s any good before forking out for the extra features of the pro. Looks interesting. I have never used my polar scope as I’ve always had trouble making out what’s what.
I've seen this app being used on an EQ mount. There was a perspex bat that fitted onto the mount dovetail holder and supported the iPad square to the mount. I think it was the meridian function on the pro version.