I purchased the Ricoh Theta V and Insta360 One at the same time to try them both out with the intention to return the unit that I liked less. There are definitely pluses and minuses to each unit:
Ricoh Theta V
* Superior form factor, probably best of all 360 cameras - Easy to hold and point with or without a selfie stick. Unit will stand on a flat surface on its own without a tripod. However, the plastic casing is slick, and the unit can be easy to drop. The buttons are tiny, and are recessed into the body, so it can be difficult to find the right button by touch in the dark. The Insta360 One on the other hand is even worse. The little round pill case form is slippery and hard to hold without dropping. As many other users note, it's nearly impossible to not hit the power/shoot button by accident and start shooting video, or worse yet, turn on the unit by accident and drain the whole battery. The Insta360 One connects to Apple devices via Lightning port, but the connector is too short, so you will proably have to remove your iPhone or tablet case to plug the One in. Once plugged in, the unit wobbles around. Ricoh Theta V definitely wins out here.
* The only unit under $500 with an external mic input - To me, this is crucial because I use the camera to record loud live rock band practices, and no internal set of mics is going to be able to handle the sound pressure levels. The Theta V also has a custom 4 directional external mic for sale, but I haven't tried or purchased it. My one complaint is that they put the mic jack in a stupid place; on the bottom of the unit. So to plug in a 3rd party external mic, Theta V must be mounted on a tripod. But wait! If you attach Theta V to a standard tripod mount, it completely blocks the mic port! You'll have to get an adapter to be able to mount the Theta V and use an external mic at the same time. The custom 4-way mic is ridiculously expensive. Insta360 One does not have an external mic jack. Comparing both unit's internal mic sound, with low to mid level sounds the Theta wins because of its 4 built in stereo directional mics. The sound is also clearer. However, when the sound level increases, Theta V seems to distort faster, while One attenuates bass frequencies in an attempt to not distort the preamp. As the sound gets louder, Theta V is completely distorted. One shows some signs of clipping at the highest peaks, but still retains the general character of the sound being recorded, altough all bass gets attenuated out of the sound.
* Great 4k picture for videos in good light - Outstanding in good light, but like all other cameras, performance drops a lot in low light. Both Theta V and Insta360 have great 4k in good light with Theta V probably being better. In low light, both suck, but maybe the Theta V is better.
* Stitching is very good - Works pretty well, but can still see distortions once in a while. The Theta V's stitching seems to be better in general to my eyes.
*Theta V utilizes internal storage which is a big minus. You'll have to keep transferring huge 4k files off the camera during video sessions which is stupid. Using internal memory perhaps improves response time, but who cares when you run out of space so quickly?? Insta360 one uses Micro SD, so if you run out of space, just pop in another card.
*Live Streaming - Theta V claims it supports live streaming, but you have to connect the unit to a computer via USB cable or some nonsense. Didn't bother to even try this feature, as there is no way to spontaneously live stream a 360 degree video. Insta360 One live streaming works pretty good. You connect the unit to your iPhone or iPad then choose live stream in the app. After giving the proper social media permissions, live streaming works terrific.
App Software - Theta V has very basic editing app. Insta360 One has one of the best editing apps of all 360 degree cameras. It allow you to change positions within the 360 degree field of view and do Matrix-like "bullet time" video sequences. The One is far more robust in its software and features.
Battery Life - I haven't tested how long each unit lasts, but both units seem to drain their rechargable batteries pretty quick. Both can be charged while in use via mini USB cable. The caveat for Theta V is if you have the unit standing or on a standard tripod mount - the USB port will be blocked.
Would I but the Ricoh Theta V if it was stolen? Yes, reluctantly. In fact, I did get my first Theta V stolen, and that's why I'm here buying another one.. reluctantly. It's good enough that you miss it a lot when you don't have it, but spending another $399 on this thing with it's little quirks and subpar low light video makes it a luxury replacement if you have the extra cash. I would not buy another Insta360 One if it were lost or stolen. But it is good enough to keep the one I have in addition to the Theta V, as it does some things the Theta V is bad at, or doesn't feature at all such as live streaming and "Bullet Time", and pivotal editing in software.