We sell the engenius and have a lot of customer problems with them. (I have personally experienced: self de-registering, loose/poor battery connection shutting off the phone, belt clips that break easily, displays losing numerous rows or columns of pixels or fading to the point of being unreadable, poor service from canadian distributor.)
They do have nice range, but Voyager is marginally better. Our tests using the same omnidirectional antenna at 20 feet fed with 9913 was 2.2km on engenius, 2.4km with voyager. Beacuse voyager uses analog (F3) modulation, it tolerates weak signal better. However, from a practical use perspective, for all intents and purposes, you may as well consider their range more or less the same.
Engenius is heavy and a some users don't like it for that reason.
Voyager does not have an easily swappable battery from a daily cycle perspective, plus the drop in charger DC coax power point can be pushed into the charger's case if you're not VERY careful with it.
Engenuis is relatively secure in its digital transmission system but audio quality is less natural. It also has a nifty 'handset to handset' full duplex walky-talky mode that some places actually use.
I would not call either of them heavy duty nor would they survive long in a rough use environment.
My two cents.
Pat