It might stop the arguing slightly. Why not tell me WHY split fins, or jacket BCDs are bad. And at the same time, tell me What they are GOOD for.
split fins have no real scientific founding in terms of being more efficient than paddle fins, are not as maneuverable as paddle fins and are very expensive. If you are just snorkeling around, are out of shape, and just want to meander around while flutter kicking then they're good enough. In scuba where you have to move around a bunch of gear that is about as hydrodynamic as a parachute, then they don't offer any power to move you anywhere and you are kicking more often *albeit with less effort* than someone who has paddle fins. You also struggle going backwards, turning around, and doing any sort of anti-silting kicks. Important when on delicate reefs contrary to most scuba instruction. Can you back up in them? yes, but I can also backup barefooted in doubles, so anything that makes my foot bigger is going to assist in that, but it takes a lot more kick cycles to move around than it does in a paddle fin.
I used split fins for about 2 weeks after I fully lacerated my calf because my calf muscle was stitched together and I needed to teach with something on my feet. I didn't have access to less stiff paddle fins, and I borrowed some split fins.
Jacket bc's are less than ideal for a myriad of reasons.
For rental fleets it means you have to have a bunch of different sized bc's for the customers/students than you would if you had a rig that was adjustable which increases your overhead cost.
They are non-modular so if a component breaks, you basically have to throw it out and start over. The lift capacity is determined by the size of the jacket, not the lift requirements.
This is particularly problematic for smaller people diving in colder water where they need more lift due to wetsuit compression and/or tank size.
They are surprisingly expensive as compared to either bp/w's or some of the back inflates. Dive Rite Hunterpac is my favorite of the back inflates and is $400, Deep Sea Supply is probably the best BP/W out there and is $500, while a Scubapro Classic is almost $800 and is a 20+yr old design....
Vast majority don't have provisions for a crotch strap. Two problems, one is ability to use a DPV which isn't really a big concern, but it's there. I've had some people at quarries ogling over my DPV and will let them take them for a spin if they have a crotch strap, but the ones that are in jackets are SoL. The bigger one is overall comfort of the rig. The crotch strap allows you to have a tight waist strap but loose shoulders which keeps the rig from moving around, particularly at the surface where you "sit" on the crotch strap similar to a climbing harness and chill out. Without a crotch strap, you have to cinch the shoulder straps to keep it from moving around and that can be uncomfortable for people when they feel restrictive.
I know of at least one instructor that has had a student with anxiety problems and the "squeeze" from the jacket helped to alleviate her anxiety which is about the only pro for that design that I can think of and is most certainly an exception to the rule. Most everyone else I know of much prefers the freedom of the harness system.
Since I don't dive them, I really can't say what else they might be good for. I hope this helps. 
