The Aeris Savant is the same thing as the Oceanic XTC-100, and like UP said, once you've got it violated, it goes into gauge mode but doesn't lock you out from subsequent dives.
The Freediving mode of the Mosquito is pretty much the same as the Gauge mode, except that after a certain time (I think 5 minutes was mentioned in this thread), it will think "Hmm, that's a pretty long freedive" and begin to display "Er". It won't lock out, though; I managed to use mine for 4 dives over two days.
I use a Vyper myself, and prefer it over the Stinger because
1. It's got an easier to use push-button menu (Stinger takes some getting used to, but no biggie)
2. It's got that simulator mode; I did a comparison between the Vyper's sim and GAP Planner -- the deep stops generated were not the deep stops I expected, and total deco time was higher by about 30% on the Vyper (I forget the profile I ran now, something like 25 minutes at 200, or something like that; around 60 minutes on GAP and 80+ on the Suunto). As mentioned somewhere in this thread, it's not really a deco computer anyway.
And if you run it in computer mode, yeah, it IS a bit on the conservative side. Another interesting thing to note is that the color graph on the left side is not a graphical representation of nitrogen loading (as with the Oceanics and US Divers), but more like a "warning light" of how close you are to deco, e.g., if the bar is all the way up into the top red, you're less than 5 minutes from deco. As you ascend, depending on no-deco time, this bar will back off gradually toward the green.
3. It's got a bigger display than the Stinger; easy to read. The logbook and bookmarking functions on the Vyper are pretty much the same as the Stinger.
True what UP (was it?) said about snagging when gearing up; I just deal with it by putting my left arm (where my gauges are) in my harness first. Also, I've removed the rubber boot that comes with the Vyper, making it a bit lower profile than with the boot.
The plastic shield can be removed for cleaning, btw; I just use my watch strap (a Trident replacement strap), slide it under the wide side opening, and push it in until the shield snaps up and out (it's difficult to try and just pull it off).
If you do decide to get a Vyper, take note: the black units are imperial, the green are metric, and the silver/gray are switchable.
A final thing on the Vyper: as mentioned, if you use it in Gauge Mode, you can't switch modes for 48 hours after your last dive. If you use it in Nitrox mode, you can't switch out until the desat timer clears, although you can switch O2 percentages. If you use it in Air mode, same thing, though -- you can't switch out (not even to Nitrox) until desat clears. So if you dive Nitrox every once in a while, best to keep your Vyper on a Nitrox 21% setting when you do air.
Oh, one more thing you can consider as a bottom timer: as another backup, I use a Citizen Aqualand. Depth and dive time info, ascent rate alarm, depth and time alarm during a dive, automatically enters dive mode, and logs up to four dives (time in and out, max/average depth, dive time, temperature).
Haven't used a NiTek3 myself, but a friend of mine does, and he loves it. Screen's a bit crowded he says, but not bad. Have you seen the VR3 10-gas computer coming from OMS? Looks promising.
Ciao.
. I'll have to do some price shopping. 
