Feickert Protractor - anyone use one?

Yes, but ANY alignment tool is worthless if you have not accurately set the P2S distance in the first place. This (difficulty in locating the pivot point) is not a flaw of the Feickert; it is a flaw built into the tonearm by a designer who neglected to account for it.  I actually believe that the Feickert (I have the older original version that uses a white plastic platform shaped like a full size LP, not the newer one that uses a black platform which is about half of a circle in shape) is better than most protractors for helping to precisely set P2S, so long as the pivot can be located with accuracy.  I also own a UNItractor, which is yet another much more elaborate take on the original Dennesen.  For its high cost, the basic original UNI does not incorporate a measure for P2S.  I was offered such a device as an accessory, for a mere $395 additional.  (In fairness, this issue may have been fixed in later versions of the base UNI.) Anyway, I use the Feickert to set P2S, and then depending upon how anal I want to get, I may use the UNI from there forward.  I also have a metal Dennesen, which sits in a box.  

Good point Lew.

Actually I've utilized my Dennesen to precisely locate the spot to drill to mount an arm.  With the P2S dimension given by the arm manufacturer and a steel metric ruler I set that distance on the Dennesen.  Then placing the alignment plate on the spindle I can swing the device to identify the arc on which the arm should be located.  From that I chose a position on that arc which best accommodates the arm and mark that point to drill.

All this seems obvious if anyone owns a Dennesen or similar alignment tool, but those considering buying one may not realize this extra benefit of this type of alignment device.  

I guess I did not make my point very well, but for me the beauty of the Feickert is the cross arm that is graduated in mm, with a vertical spike at the far end that can be set down on the pivot point exactly.  If you measure P2S with a conventional ruler of any kind, there is that awkward requirement to estimate that you are "over" the desired location of the pivot; if the ruler does not lie in a horizontal plane parallel to the pivot point on the tonearm or the blank tonearm mount, there will of course be an inaccuracy due to parallax.  The Dennesen and even the original version of the UNItractor, incorporate cross arms that are not marked in units of distance.  (I am guessing that this fault has been remedied in newer versions of the UNItractor, because I think I see in photos that the SMARTractor includes a crossarm marked for distance in mm; the SMARTractor is less expensive than the UNI.)

Amen to that lewm !
There are a FEW TT's with something sticking up from the pivot you can sight on with a 50 buck Geo-Disc and get 'er done but not many .