-Normal shot clock is no good because unless pool becomes a huge dollar sport its not feasible to have a ref with a shot clock on each table.
-Chess clocks sound like a better idea. However, for as many years as we've all talked about them, I've yet to see a tournament use them. I actually tried it once in a gambling one pocket match with a buddy about 20 years ago. He kept forgetting to hit his button and about threw the clock at me, ha ha.
Also with a chess clock, there could be a situation where it just happens to be a long game, but neither player is a slow poke. Score is tied 5-5 and the balls are out of play. Player one has 1 second left, player two has 2 seconds left. Why should the 1 second left player lose? Neither player could possibly win.
One pocket in particular is also a game where a lot of the time the shots are short and quick moves, like tapping a ball a bunch of times before someone leaks an opportunity. The players in this scenerio simply stand at the table while the opponent is shooting. They don't go back to their chair. Sending the players back to their chairs to press the button each shot would probably ruin the flow of a lot of games.
-Grady rules are different every event, and hard to remember. How many balls up table before spotting? How many get spotted? (those are rhetorical questions). Also with Grady rules they can surely speed up a match, but the players could simply knock all the balls up table again and repeat the whole process over and over. There is not a definitive expected end time to the match, in order for the TD to schedule rounds in advance.
-What I'm proposing (and what Pat is doing on his International Open Amateur Event), is the best scenerio for a TD, IMO. Its simple. No special equipment. Can be used at any tournament, whether local weekly or national level. Does not alter game-play until it is used. Has a very quick ending once it is used. Gives the advantage to the player leading the match. Still requires offense once it's started, which takes away most (but not all) of time clock manipulation beforehand. Ensures definitive time predictions of matches.