>>4090671Always better to get the longer lens if you can. They're fine if you occasionally just need more reach, but for serious use, I would upgrade existing lens lens.
>>4090744Most 1st party ones have a bit of the optic that sticks out, and then physically will only fit certain lenses that have the space. They basically make them for the lenses that are intended to be used with a TC.
Most 3rd party don't have that part that sticks out, so you can mount most any lens, but quality is often not the same and you may run into other issues. They cut light, so depending on the camera and lens you can definitely run into issues where the camera struggles to focus, if at all.
