We've had the opportunity to borrow and own a few thermal devices. Our experience with thermals is pretty limited to be honest. I'm just going to go over the ones we've had a give our input based on this.
We've used the older FLIR HS-307 65mm (video is on You Tube). It had an impressive image and the 65mm really reached out but it's too large to be used as a handheld in my opinion. It used a lot of AA batteries and the only way to externally power it was using a hot shoe and cigarette plug. We used it that way from a vehicle and it worked good in that regard but compared to what's out there now in 2019 it's pretty dated. This was a borrowed unit.
Next we bought the FLIR Scout TK handheld monocular. This isn't a terrible device for the casual user around the yard or camp who isn't looking to go hunting hogs or coyotes at distance. It has most of or all of the popular FLIR palettes. It's fixed focus so that combined with the small sensor depending on the range the images can be pretty blurry. I wouldn't recommend paying full retail but a used one at a good price may be worth it for ID'ing under 50 yards and detection under 100 yards. It's light and small and fits well in a pocket or inside a shirt/jacket. It didn't fit our needs so we sold it.
After that was the Pulsar Trail XQ38 weapon sight. This thing is awesome. Worked very well as a thermal scope and wasn't terrible handheld. It came with the Pulsar QD mount and the mount did an excellent job maintaining zero. I used it almost exclusively handheld using a picatinny rail with sing swivel to hang it on the neck. It's fairly large and can swing around a bit so you need to be careful not to hit it on something. The 2.1 base magnification worked well but for distances we scan at our property it was borderline too much magnification. It only has black hot/white hot modes which work very well but we really liked FLIR's outdoor alert mode for making animals really pop against vegetation. You can wifi it to your smart phone or tablet and use an app to view the image, make adjustments, etc. It also has internal video recording with sound and photos. We sold the XQ38 in order to put the funds towards the N-Vision Optics PVS-14's we bought with L3 filmless white phosphor.
I was loaned a FLIR Scout III 240 to try out and buy if I liked it. It was a very generous offer and I thank the fine gentleman for doing that. It's a decent handheld spotter. The display screen is small compared to newer thermals. The 320 sensor does well within 100 yards. Like the TK it's fixed focus and images can be blurry. The S3 240 doesn' have any video or photo recording capability. It would make a good spotter to go along with a thermal weapon sight for hog, predator, and varmint hunters. This allows you to use the Scout to look for hot spots and then switch to the weapon sight so you're not waving your gun around looking for stuff. I decided to return it and get a thermal that could be handheld and weapon mounted. Get more bang for the buck.
The device I picked and we're using currently is the FLIR PTS233. Like the Scouts, it's fixed focus so images can be a little blurry but overall it does very well to ID most animals up to 100 yards. A person, no problem. It'll detect well beyond 100 yards. The furthest I've been able to detect a heat signature so far has been at about 300, although I haven't had opportunities to see something beyond that yet. It works great as a weapon sight and the QD throw lever that comes standard does hold zero. I've confirmed that. The newest outdoor alert mode works extremely well. It's also easy to add an external battery pack. It's much smaller than the XQ38 and hangs on the neck better. Like the Trail XQ38 it has internal video and photo recording but no sound. You can also connect to a device to make adjustments but no live image view. It has some minor annoyances such as the buttons are a little hard to push but overall both I and the Mrs like this one the best so far.
If you're looking for a thermal device I'd recommend starting off by deciding your budget first. Second, decide what you will use it for primarily. For instance, since we use ours mostly handheld, it was important we select features well suited for that. Once you establish these two criteria you can start researching the different devices on the market in your price range that fit your primary needs the best.
There are several great manufacturers producing excellent devices and it looks like there's only more to come. If you're not sold on any particular device, I'd just wait it out and see what's coming.