As someone who has actually taken the Essentials class, I can tell you that non-split fins are required because
one of the stated goals is to learn to do the standard kicks: frog, modified frog, back kicks and helicopter turns. Believe me, back kicks are tricky enough in Jetfins.
FWIW, other objectives of Essentials include buoyancy, trim, buddy awareness, detailed gas planning/rock bottom calculations, min deco, the basic six*, shooting a bag, blue water ascents, valve drills, toxing diver recovery, etc.
Buoyancy, trim, and non-silting kicks are critical to successfully mastering the other objectives since they will be done around 1 foot off the bottom, which has a way of highlighting loss of buoyancy control during, for example, an air share or even a mask remove/replace drill. And, of course, the camera doesn't lie.
Likewise, to do the drill where you guide your maskless buddy back to the line or entry point, or the drill doing the standard six minute ascent with a buddy on an air share
while maintaining horizontal trim is
not going to be comfortable (or even reasonable IMO) on a standard regulator/octo combination. A minimum of a five foot primary with a bungeed backup is going to be required to complete the skills and objectives of this class. I can tell you that I usually dive a five footer for single tank diving, but I was glad Jeff encouraged me to bring a seven footer for the class. My teammate used a five foot hose and at the end of the class wished he had also used a seven footer.
Regardless, I can tell you there is quite a bit to cover in a long weekend. I was glad to have a team member in the class who was as serious about learning in the class as I was, and went into it with commitment to learn and a great attitude.
John_B
* The basic six drills are: reg remove/replace, reg exchange, reg recovery (both reach and sweep), mask flood/clear, mask remove/replace, and the ubiquitous s-drill.