I'm currently toying with looking at one to help with perhaps a unique issue. From that perspective i'd say just look at why you think you want one. In terms of the device itself, they can be fiddly to adjust and setup, but fit is important. Some prefer a loose fit that's more accommodating to a variation in position, some prefer something more specific, less adaptive. But they seem to hold their money so I doubt you'd lose much if anything on the experiment.
BFTA/NSRA County Coach
CSFTA Chairman/BFTA Rep