It's been a while so I thought I'd add an update. Have been using the iPolar to do alignment successfully over the last 6 months - on a clear night with the right gain settings it just sails through alignment with the caveats previously mentioned even in a light polluted UK city suburb.
However just recently I thought that the indi libraries and kstars version should really be upgraded from the default raspbian repos I used initially so cloned the PIs flash card and ran some upgrades to indi 1.8.9 and kstars 3.5.2 from the astroberry repos in order to get the new polar alignment features and stellarsolver and it's fair to say the results were not positive.
The image now coming through from the ipolar is noisey as hell and solving fails completely against it, can't even get it to acknowledge there are stars in the image regardless of gain settings (solving works fine and super rapidly against the main camera although the image displayed in the solving screen is noisey).
So I recloned the old card, left the old version of INDI in place and only upgrade kstars - same problem! I haven't had time yet to go back and step through versions of kstars to see exactly where the problem occurs (There were a number of other oddities with kstars including the slew rate it tries to use on the iexos-100 mount we have) but right now I'd have to say that in terms of using the iPolar then all my comments previously about getting it working relate to Kstars version 3.0.0 and nothing newer at this time!
I can't offer any more data at this point as I bgot stuck in a library mess after upgrading my pi so completely rebuilt it, however around the same time we acquired a guidescope with a QHY camera so we have been using that for polar alignment as it is one less USB cable to manage!
If we get some clear nights soon I'll do some testing with the ipolar and see if it's any better with my cleaner build of the libraries.