My view - they are largely OK for a bit of fun, but take the results with a pinch of salt. Different browsers can make a difference, so running the same test on Firefox and Chrome one after the other is likely to give you quite widely differing results. Pings reported by Ookla tests such as you get on
http://speedtest.net/ can definitely not be relied upon to be accurate - the best way to ping something (assuming it can respond) is from a command line/prompt depending on the OS you favour.
The only speed test that has any actual relevance is the
BTwholesale one, as that is referenced in fault reporting if you do have a speed issue. It can also give you your line's IP profile, which again is useful for diagnostic purposes.
Do the Ookla tests (of which there are many) if you like, but don't rely on them for accurate diagnosis.
