I use it every day, on perhaps 4/5 different EU's and different BB products. I have been doing so for many years now.
I don't work to decimal points, haven't really got the time
, but I will show the EU the connection speed of their router via our WHOOSH system, and explain that on a wired connection they should be getting a percentage of this (roughly 94%), but always explain that being anal about it will drive them to an early grave.
I genuinely can't recall anyone questioning the speedtest.net result ............ they're more than happy to have gone from poor speeds to very fast speeds, and the results are always there or thereabouts the 90%+ area.