I would never return to Otto.
I compared prices on an oil and filter change for my 911. After checking five or six independent porsche mechanics in the area, Otto quoted $200. 33% more than the average of five others who were at $150 - $165. (The dealer was $225.)
I sent a friend to Otto for a major tuneup recently and Otto who was several days late returning his car, was unable to fix a simple electronic problem and charged far more than the original estimate for less work done and much more than the dealer would have charged for the same 30,000 service. (Apparently he is not familiar with the increasingly computer and electronic nature of porsches over the past 5 - 8 years). The electrical problem was quickly fixed at a neighborhood gas station mechanic.

I have found him argumentative, and overly generous with his intolerant opinions about women, other porsche mechanics, and people of different 'backgrounds.'

He may be good for older model porsches, 1985 and earlier, which is mostly what you see at his shop (overly crowded, dirty, and his office is filthy, too dirty to sit down in if you are wearing clean clothes.
I would never return, but if you have a vintage porsche, you could take your chances.

Otto's is the "go-to" place for vintage Porsches, specifically 914's. My little 1972 914 has been with me for a lloonnggg time. It has come a long way with Ottos' help. ...