My dob is finished, the mirror arrived and I tried it out last night ... the results were pretty good. Managed to find m3 (under Bortle 8 Minneapolis skies) and the stars were nice tiny points, although the view was rather dim and required averted vision to get the full globular effect.
Have to say the skies here are a bit disappointing so as a result of that I will probably do a lot of moon and planetary viewing.
Right now my highest power is a 9mm plossl ... have a meade 4000 6.4 plossl coming from ebay (only 24 bucks) so I will do some star testing and lunar viewing with that when it comes.
With the 9mm (x169) the point of best focus was obvious ... I would stop short of saying the mirror has a hard "snap" focus, but it's close. Higher power will tell more and I can do star testing. I tried some star testing with the 9mm and the out of focus image on either side of focus was very similar.
Overall I was pleased with the performance and for $535 from Agena Astro (with free shipping) it seems like a pretty good deal. I passed on the GSO secondary bundle and got a 2.6" 1/18 wave unit from Astro Systems.