Divergence is normally a pretty tight spec, if it falls far outside then the unit will not perform as advertised.
Remember, the Vector IV is more than 20 years old, and it has a 1550nm laser. That uses MUCH more power than a typical 900nm commercial unit. You need about 50% of the beam on target to get a reliable range, unless the unit does multiple ranges, which the Vector does. The IV will get a good range on a 24" square target at 2000 meters. The 21 has a .7x.3 mil beam and will ping the same target at 4000.
Beam shape can be an issue, with a narrow but wide beam, your device is setup to range critters that are wide but not tall, like deer, elk and so forth. It would not be optimum for tall targets, like prairie dogs or people. You can of course change the device orientation to get the beam on the target, say you need to ping a telephone pole, turn the unit sideways so the vertical portion of the beam is oriented on the target axis and you get a range when held horizontal it misses.
really small beams SEEM like a good idea, right up until you find out the device is not perfectly collimated and the reticle is not where the beam is. Then it's a challenge to get the beam on the actual target, because of parallax error between the emitter and reticle plus lack of collimation.
As someone once said, it's complicated.