When i first started making fluidy things my computer was pretty slow so i did a lot of testing on collision types.
it seems plausible at first that having a custom collision polygon with less side# would make the simulation faster, but thats not exactly the case. the physics doesn't have trouble handling points/ edges etc, rather the collisions between objects/points/edges are what cause slowdown. having a triangular or square shape can cause the "particles" of fluid to catch each other and make extremely large slowdown spikes when "compressed", not to mention unrealistic stacking behaviour.
using ellipses actually fixes EVERY problem, circles seem like "higher fidelity" shapes to process, but the reverse is actually true, an ellipse is very simple, and can be defined and have collisions tested against it with one simple distance check, and a few trig functions like sin and cos. checking if two spheres at any angle collide is as easy as checking the distance to see if its less than the sum of the two radii.
you can have WAY more circular colliding physics objects than any other shape, because they're so simple to process and check, so put on those ellipses!
the only problem with this method is the ellipse shape in the physics plugin assumes you want the ellipses to have the width and height of the graphic, the way around this to get the quaziblob effect to work is by using one object for the physics, and putting a separate graphic sprite thats larger in a container with the physics object, then setting its position to that of the physics objects every frame.
like tul said, this is because the visual effect is only 5% the size of the meta-gradient graphic that makes the whole effect work