I have an EMC-20H. It is liberal and will get you out of the water faster than just about anything else on the planet with a 0% conservatism. If you dive tables and use the computer for back up, it is not a bad way to go if you want an absolute minimum time to surface in the event a storm is brewing, your buddy went missing, etc.
But for regular use I think divers would be insane to run it lower than about 30%. Personally I have mine set at 60% to keep the profiles similar to the sig other's VR3 or Nitek Duo.
One of the best features of the EMC-20H is the really easy never going to forget it automatic gas swithcing.
One of the worst features however is the automatic gas switching. It is a non-problem in offshore diving but in a cave it can get interesting. For example if you are at P1 and want to go to Challenge sink the hard way up the Olsen tunnel through Olsen sink, you will shallow out at 5'-7' at Olsen and the computer will switch you to O2 unless you set it so that the bottom time has to exceed X minutes before the switch occurs. Coming back it would be the same way (and it would get really crabby with you being at 65' on what it thinks is 100% O2). So you have to pre-set the computer based on the plan. In this case you'd need about to set it to need to exceed an hour and a half of bottom time before allowing a gas switch.
So if your first dive was at Little river where you get into deco a lot sooner than that, you need to set it for dive one, then reset it for dive two. And that is a bit of a pain to do manually so it is easier if you bring along your lap top. Switching from He to Nitrox is, as far as I know, not possible to do manually without the laptop.
I tend to work around it in the example above by doing dive 1 with O2 programmed and on the deco, but then just set gas 2 to the same 32% as gas 1 for dive 2 and eother skip the O2 use on deco or use the O2 for deco for the slightly longer 32% deco the computer is following. There may be an easier way, I have just not found it yet. (I'd love to be able to turn the auto switching on or off while in the water)
So if you are computer savvy and carry a lap top with you on your dive trips, at least the cave trips you'll get along fine with it. Otherwise you'd be better off with a VR3 or a Liqivision.
For a rebreather diver the PO2 options are great, but the EMC-20H is not well suited if you revert to your bailout gas and want to deco on that.
I am a relative EMC-20H newby and Phil Ellis is the guy to contact for EMC-20H tips and info. Its on my list to do when I remember to do it.
As indicated above at 60% conservatism it stays in the same ballpark as a VR3, but I noted on a week long 2-3 deco dives per day trip that it started getting much more conservative on dive three than the VR3.