I have had great success with a generic KVM I found on amzn [0], but it now appears to be unavailable, which is a shame because I wanted to buy another. Perhaps I can find it somewhere else. It has never failed to switch between sources and the only delay, as some others are pointing out, is the HDMI handshake process inherent to the monitors themselves.
I did have a considerably more expensive TESmart [1] but couldn't use it because it had some weird incompatibility between it, thunderbolt docking station [2] I used with it (which also work flawlessly), and the MBPs connected to it. I could never figure out why, even raising the issue to support with no luck.
You don't feel skeptical of products from a company called "GREATHTEK-More Convenient"? I am far too paranoid to plug random technology like that into my computers. It makes shopping for such things on Amazon nearly impossible.
Given that GPU cards tend to have more DP ports than HDMI ports, why might that be? Why don't makers of KVM switches follow the same preference as GPU's do? (or vice versa. Why do we have two standards anyway)
I did have a considerably more expensive TESmart [1] but couldn't use it because it had some weird incompatibility between it, thunderbolt docking station [2] I used with it (which also work flawlessly), and the MBPs connected to it. I could never figure out why, even raising the issue to support with no luck.
My two cents.
[0] https://www.amazon.com/gp/product/B088WGKFZH
[1] https://www.amazon.com/gp/product/B08N494N7X
[2] https://www.amazon.com/gp/product/B08HR3T837