i'm using a steadicam merlin without a vest with a panasonic AF100 camera (and sometimes with a GH3). I did a lot of furniture-exhibition videos with it (see
http://youtu.be/Rbvenk5FApk for exampe - some might have been filmed in 50fps converted to 25 and/or additionally stabilized in fcpx), where it allowed me to be much quicker and make more interesting images than with a regular tripod.
i once tried a glidecam without a vest with similar results im steadiness (but not quite as good). i also tried the glidecam with a vest - it didn't add anything to the stability but required less strength in the arms to operate (but put a lot more stress on my back - i, for once, prefer the pain in my arms

!). i'd definitely go for the merlin over the glidecam because it's lighter, smaller, has better built quality and takes a lot less strength to operate because the weight rests directly above your hand. also, you can fold it, so it takes less space when transporting.
on the downsides: the merlin doesn't take as much weight (but seems to work with lighter cams than the glidecam), is harder to calibrate, probably easier to destroy and you can't reverse it (put the camera on the bottom and get shots really close to the ground)
if i were you, i'd try it with and without the vest. if you're planning on operating the cam on really long uninterrupted shots (say 2 minutes plus) a vest is probably a good idea.
also, operating a steadicam takes some practice (imho the merlin even more so than the glidecam), so don't be disappointed if it's not as smooth as you'd like in the beginning, or if you have a hard time calibrating it.
as i said before, it takes me less time on an exhibition to get good shots with the steadicam than with a regular tripod. but it's not fire and forget - you have to recalibrate the cam pretty often, it doesn't work if it's to windy and if you touch something with the steadicam, the whole shot is ruined. and you can't add any gear (cables, monitors, wireless audio) to it without recalibrating it (5 minutes if you're quick, usually more like 15-30 min, i would't want to calibrate it to a new lens while in the field) - so it's probably never "the quick over the long". it's a pretty cool tool that gives you a lot of opportunities for shots you'd otherwise only get with cranes, sliders & dollies, which take even longer to setup) - btw. obviously you can't touch the cam while filming, so no focus changes without a wireless follow focus) - but it's not a universal tool.
i use it for exhibitions, image-films, music videos & drama. i wouldn't recommend it for concert shots (too long uninterrupted shots, usually not enough space to move uninterrupted), lots of outdoors work (wind), anything that requires touching the camera (in camera audio, manual focus changes, manual zoom) and situations that require you to be really quick (like ENG work)