A lot depends on the user. I have shot over 1300 coyotes in the last 4 coyote seasons. The majority of these are using thermals in very wide-open country. I have been doing this for a lot of years, so experience with the same thermal of similar FOV and magnification can help. I didn't know if a LRF would really help me or not as I moved to the
Bering Optics Super Yoter LRF this year.
Is it night and day, the difference in how many coyotes I kill, no? Does it mean a few extra coyotes in the back of my truck at times, yes but a big reason for the smaller impact is my experience with thermal hunting. However, for a new nighttime coyote hunter the difference is larger. The majority of all nighttime coyotes are killed inside of 200 yards. A person doesn't need a rangefinder to shoot 200 yards with most modern centerfire guns. For me, the main situation where it helps is with multiples. After the first coyote is taken, too many people in my opinion open up and mag-dump on the remaining coyote or coyotes. Personally, I will normally wait for a few seconds, hit them with a sound they can't resist and stop them. This is the 2nd or 3rd coyote when they have run out a distance when it really helps. Guessing 275 vs 325 yards or the other way around is probably a miss even with the flattest shooting calibers.
The LRF provides confidence because it always nice as you are calling in coyotes to know when a coyote has gotten into point-blank range. Any shots taken from here on in are going to be aiming with no adjustment or hold-over. There is also the occasional coyote that has been educated by hunters that will stop at longer distances or attempt to do a large circle around the sound source. In these situations, a rangefinder can also be very helpful.
This was a long answer to say, for a new user given the choice of 384 with LRF and 640 without, I would probably lean towards 384 with the LRF. The better answer is 640 with LRF, but I realize this isn't in everyone's budget.
One of my roles with Night Goggles is helping people find the right thermal for them. I will send you a PM with my direct contact information. I don't work in sales and don't get paid by commissions, so I will shoot straight with you.