Oh, I see the confusion. I have no issue with iburst and pool. Usually.
To back up a tad, iburst sends an initial flurry of time requests to the
chimer. This primes caches from here to China a back, fills the DSP/PLL
loops with data, and through various mechanisms, gets ntpd closer to
"correct" time quicker than normal on startup.
Note the detail: quicker on startup. Otherwise no effect.
The problem at hand is that a user has local PPS and wants that time
to win the startup race, ahead of the more jumpy network chimmers. It
is maybe 1,000x more accurate and stable.
To that end, a user places the PPS at the top of the ntp.conf, with a
short poll time than other refclocks, so that ntpd will select it first.
But, when you add in a bunch of marginal pool servers, from all over
the planet, and iburst them, then they win the race instead of the nice
local PPS. ntpd starts out with the worst refclocks, not the best.
Eventually ntpd will sort it out, usually, but best to just pick the
local PPS on startup.