In divisions with tube fed shotguns, it will be rare to find someone at the "top level" using a pistol grip.
In open division which allows box fed magazine shotguns, it will be rare to find a gun that doesn't have a pistol grip at the "top level"
If we look at IPSC shotgun, where the sole focus is performance with the shotgun, there were basically none to be found being used at the past few world championships in tube magazine divisions.
Out of hundreds of competitors from around the world, if there was one in use, its wasn't due to trying to gain a performance advantage over everyone else, and they were not in contention for a spot on the podium.
For the OP,
Definitely use what you have until you get the experience to know what you want and need in your equipment, then you can upgrade accordingly.
Haha exactly my thoughts! Basically if ur quad loading then sure, i agree the pistol grip gets in the way and requires time costing hand changes. But for a box mag fed shotgun a pistol grip compliments it like a spoiler compliments a Formula one car.