My dad had a wonderful spark tester. He would call me over and say,"Hold this screwdriver." Based on how high I jumped he knew how good the spark was.
I have taken a direct hit from a Wisconsin magneto, won't soon forget that one. I use the first one mentioned and have had no problems, I have one like number two around here somewhere but don't use it much.
Style #1 tester is convenient to see if the spark is "missing" or "cutting-out" while the engine is running. ....It is easy to hook up in series with the plug wire and plug.
Style # 3 tester is quick, convenient, and accurate. ...If the spark is not strong enough to jump the oversize gap, the ignition system is weak.
The most unusual spark tester I've seen was named Eric Bloehm. ...He worked for us back in the 1970's, and I'll never forget him. ...He would hold the plug lead while turning the flywheel by hand. ....If the muscle in his forearm near his elbow twitched, the spark was strong enough to start the engine. ...If the muscle did not twitch, the engine would not run.
I saw him do this on B&S, Tecumseh, Kohler, & Wisconsin magneto ignitions. ....At first, I doubted him, but a (conventional) spark tester proved him right 100% of the time.