Andrew,
certified chronometer accuracy is only at the time of testing and when the watch is sold shortly afterwards.
When the watch has been worn for several years the accuracy may have become worse (not necessarily) and then the chronometer
might behave like a non chronometer watch... so no advantage at all... but only if you compare e.g. 551 versus 552 or similar...
If you take 30 T2 Rg versus 30 T2 you can SEE the difference by the different level of movement finishing, e.g. polished crown and ratchet wheels,
special regulating device, etc., compare Cal. 354 with Cal. 352 to mention an automatic chronometer, although Cal. 354 was also delivered with chronometer
specification - see different inscription on the oscillating weight - but this is all... all the other parts look quite the same as on a regular Cal. 354 - so no advantage there...
If you take Zenith for example - the famed Cal. 135 was only built as chronometer - there is no comparable Cal. by Zenith... so you buy a rare (low production number) and
beautifully constructed and finished movement.... all the advantage here!
I hope I could shed some light on this topic...
regards
Erich