I went from an EMC-20H to a Predator SA and breathed a major sigh of relief. The EMC-020H is ok in open water and if set anywhere near the liberal end of the conservatism settings, will get you out of the water faster than just about anything else on the planet. I would not recommend anything under 30% for conservatism.
The EMC-20H runs into issues when you can't control the profile - as in cave diving - due to the automatic gas switching. It takes a great deal of effort, pre dive planning and exact knowledge of the cave profile, dive times, etc, to defeat that less than desireable feature to prevent it from insisting you are on a shallow deco gas when you are really on back gas.
The display on the EMC-20H is much harder to read and in fact about 20% of male divers out there have a great deal of trouble reading the display on the red black lighted EMC-20Hs.
The Shearwater takes an entirely different approach. First, the OLED display is stunningly easy to read even with middle aged eyes. The Predator is very simple in over all layout and operation, is intuitive to use and has an excellent user interface that allows full programing on the unit in a matter of a minute or so. It also does not automatically switch anything and assumes you, as the diver, actually have the brain and know what the gasses and settings should be. It will advise you when you can make a switch, but it leaves the decision up to you. You can also reprogram gasses during the dive if desired/needed and with one of the more recent updated, you can pre-program up to 5 gasses but then leave them inactive on a given dive, making it easier to add/switch between standard gasses over a series of dives. Shearwater is very repsonsive to user input and has frequent firmware updates that include very nice upgrades and improvements.
The Predator also has a very useable dive planning mode, and if you re-run it with each deco gass separately you can use it for the lost gas contingency plans as well.
In short, it is pretty much the polar opposite of an EMC-20H and well worth the extra cost. A key thing to consider is that a used EMC-20H is a common find, usually at a sub $400 proce point. Finding a used Predator for sale is a lot less common and they sell for a lot more money, suggesting the perceived value of the Predator is much higher.
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That said, the standard advice it to start your trimix career with a bottom timer and some type of computr softward to cut tables for the primary, contingency and lost gas plans. It gets you in the habit of also doing the gas planning rather than short cutting the process (although by advanced trimix you should have that down) and it lets you also develop a better feel for the deco curves at various depths and run times with various deco gasses.
V-Planner is often mentioned but on a laptop or netbook I pefer GAP. In the real world I tend to use iDeco on my iPhone as it is always there, very convenient to use and produces profiles you can save as text or e-mail to yourself. I recently acquired a very useable waterproof bag for it so I have no real concern using it on a boat.
