I have it, and yes it work on other cars. Did you try it on the 03 Land Rover Discovery, the SAI Valves need to be removed, which cause the air escape.

 

Yes, I have used it on a Discovery and did not have a problem with air escaping from SAI that I can remember. But as you say, you can just plug the holes in the head to resolve your issue. The tool works well but is a little tricky when compressing springs on the rear of the heads close to the firewall. On the left side the heater core pipes are also in the way, but you can work around them if you take your time.