The lovense cam is just a re-branded insta360, so if you dont see yourself using the lovense features then I would just get the insta360 cam which you will proberly be able to find cheaper.
for $300 you might be able to find a good used dslr which could be a vast improvement over a webcam. Your phone could also be a vast improvement over a webcam...everything kind of depends on your setup (lighting and such) and what you want to get out of the camera other than 4k video.
Personally I dont think any webcam is worth $300, another thing to note is that most sites dont support 4k broadcasts, and the ones that do normally have requirements you need to hit for them to allow you to broadcast in 4k. Chaturbate for example if I remember correctly require you to have a minimum of 100k followers, and there is probably other requirements too.