[Alex KL-1]

I have converted a cheap Casio TV-770 for general modern use (for easy demonstrations), but in a harder way: I build a composite video input using the original antenna P2 socket/plug. Since this set is plenty and abundant, I don't bother about some butchering.
Now I can plug anything that has same video standard as this device.
And the external visual are not changed.

Like I said, is a harder way, since most sets, even portable ones, have larger video signal amplitude than the composite video (some sets have whooping 4Vpp, and composite video and cousins have maximum 1Vpp), so it sometimes upset sync separators and color demodulators. And it can introduces new grounding issues.
For example, if the intention is to glue a mini digital converter on TV back, using same power supply/battery, the direct video option will may introduce some interference due ground currents. The antenna method will isolate the devices, since is possible to couple with very small capacitor (so is easier).
A careful ground arrangement, of course, can mitigate eventual issues in direct connection (or different batteries for each device).

So...

The pros of using the antenna method, is safer to use, is original use for >90% of TV sets (all these not having a video input).

The pros of the video input method, is cleaner images on bad calibrated sets, and sharper images on color TV when using S-Video for example.