I have a rule... never push a carto past an o-ring drip tip end first. Yes, you can get away with that with a tank tool--but what if you don't have a tank tool handy?
What if like me, you've gotten too lazy to use a tank tool? You can leave even a fat drip tip on and just push the flangeless 510 connector down in the tank, leverage the connector over to the side by pushing sideways on the drip tip and fill past the connector with a dropper bottle. When you push the connector end back up through the o-ring, there's no sharp edge to cut or shave the o-ring. Just wipe off the connector as you would after condom filling.
What if you're even lazier? I've been using straight drip tips that fit through the end caps for some time now and fill without removing the carto tank from the mod (possible even with flanged). Just slide the tank up just past the top of the drip tip, leverage the tank over to the side, and fill from that end. The straight drip tip's end protects the o-ring as you slide the tank back down.
With flangeless, it's easier to swap out a dead carto, even with a full tank, without a tool. Put the 510 connector of the new carto in the drip tip end of the old one and push the new carto in past the first end cap's o-ring. Flip the tank over and push the tank down on the new carto until the old one pops out the top and the new one slides past the second end cap's o-ring. No sharp end pushing toward an o-ring.
Besides not allowing filling from the connector end or swapping cartos as above, a flanged carto leaves a gap between the tank and mod unless the end cap is relieved for the flange. The main advantage I see to flanged is you can pull a drip tip off without pulling the carto out of the tank--and that's not an issue if you do that with the carto screwed on a mod.
Of course, this is IMO and YMMV. I'm not a fan of flanged or depending on a tank tool. I'm loving my IBTanked tanks even more with ByLeo Sophias. They're a match made in heaven.