Note that there are different quad setups:
- the one where the rears are doubling the fronts: rears positioned on the rail, close to the fronts. The PSH were set up this way. Kind of splitting twin fins.
- the ones where the rear quads are actually the central fin of a thruster, but splitted in two. Positioned thus to the rear, and closer to the stringer. This is called the McKee setup, and is now used by most SUP brands.
I will only speak of the mckee setup, I never used the other setup, but I read that they can easily make the board track if you use the wrong kind of fins for the board and your style.
However, from the pictures the loose leafs seems a kind of an hybrid: basically a split twin setup, but with the rears a tad more to the aft.
- by default, quad fin sets are geared to back foot riders, because they enlarge a lot the total surface of the rear fin. This is what you experienced. The solution is to tweak the rear fins, using smaller ones (less power on the rear foot) and ones with symmetrical (50/50) foil (that smooths the rail-to-rail transition). I like for instance the FCS2 Gerry lopez rear fins. This way you can have a good compromise: the speed and hold of a quad, the control and vertical surfing of a thruster.
- The shopping trolley turn that Piros describe is the feeling of floating (the board yaws uncontrollably) when the board goes flat in between turns. It may or may not happen, it depends a lot of the board shape. If it happens, a nubster or a small fifth trailer fin will help.
- Basically if you want speed, especially out of your turns, go quad. If you want to be able to tighten your turns and burn off excess speed easily, for instance to stay close to the pocket, go thruster. As kelly says: quads for tubes and fast section, thruster for turns.
Here is for instance a setup I like a lot (I am a front foot surfer): Al Merrick twin fins fronts for extra power and squirt in turns, and small symmetrical gerry lopez rears for control and looseness in turns. For some reason, this specific board doesn't need a 5th fin, but I had similar ones that worked better with one.