Best flash for the k-01?

Ok, need a flash for indoor family shots for the most part. Between the Pentax AF360, AF540 and the Metz and Sigma offerings, which would you go with? Seeing as I using this for family snaps, I'd rather spend less than more, unless it's just not worth it?

I've read up a lot on this stuff and am even more confused, between P-ttl and Auto, many saying Auto is better, but not remembering who has what. On the k-01, it looks like it doesn't use the flash focus assist lamp from others tests, even though manual says it does. Not even sure if this is a better option anyway.

Anyone use the bracketing function on the metz? Worth it or not?

I also know I can't use off camera flash except in manual, except if it has a auto thyristor circuit, which was briefly explained to me, but still confusing. So for my first flash for this application, what would you use?