I use this one, I think it is as accurate as most. It certainly shows my speeds pretty accurately.
Speeds will vary a lot, depending on time of Day/Night, and Contention Ratio does have some impact.
iPhone X review
Political cartoons in 2017: Chris Riddell, Rebecca Hendin and Dave Brown on what it’s like to…
The best iPhone for 2017
Tennis : comment regarder la finale de la Coupe Davis 2017 ?