I have been making yogurt for years but using either a small amount of my previous yogurt to culture, or "Bulgarian" yogurt culture that is sold online (which I have used in the previous yogurt batch in the first place).
I decided to give David Asher's method of making yogurt a try - using kefir as a starter. Well, I can report that it seems to work! Although, it is a bit on the "thin" side. However, I almost always strain my yogurt into a Greek style, anyway.
I didn't bother holding the yogurt at 185F and constantly stirring for 30 minutes as Asher suggests; I never do that with my other yogurt in the past. I generally keep at 180-185 for about ten minutes, cool to around 100, add the culture and incubate in an oven with the light turned on.
I am now straining the yogurt from kefir culture but I did taste it and it is pretty much the same taste (and smell) as my "Bulgarian culture" yogurts I make.
Another thing I did not do was allow the milk kefir to go through secondary fermentation - the milk kefir was freshly strained from the kefir grains after being on the counter for 24 hours.
Anyway, seems to have worked!