Trip report of size one, fwiw: I have a JetKVM device at home and it's been super handy in my small homelab (half dozen or so older dells and lenovos). I haven't experienced any problems with my device. It seems solidly built, the software works well and is receiving updates, and the price was very fair from what I recall. One feature that I thought was particularly a nice touch was that you can store OS images on it and have it show up as storage on the target machine (though some of my older gear doesn't seem to want to boot from it for whatever reason -- which I suspect has more to do with decade+ old workstations that last got a firmware upgrade when Obama was president than anything JetKVM is or isn't doing).
Overall, I'd recommend them. :)
Check to see if they are connected via usb 2? I know in the past I have had problems with older hardware on a usb 3 port vs a usb 2 port...