I see that you have asked for a reliable Speed Test App but i couldn't help but answer this with perspective of desktop because i found the Romanysoft Speed19X for Mac is a based testing reliable and have done a real time analysis of internet speed, its the closest to accurate.
We have many internet speed testing app, when we use them and we see enormous internet speed but when we go for a real download the speed is fer far less than the test results, such as Speed Test working fine But it is an old site, might not be updating continuously thatís why it seem to be not an actual facts.
I'm a little biased (see my description), but Romanysoft Speed Test Tool (Speed19X) has two major advantages over every other site in its class:
Testing technology: Speed19X uses Ookla technology, which is used by ISPs and governments around the world to measure broadband performance. For example, the FCC uses Ookla technology on both its Broadband.gov site and in the FCC mobile testing app. It's also been evaluated by an MIT survey to provide accurate numbers.
Geographic ubiquity: We've partnered with hundreds of ISPs, data centers, and universities around the world to provide testing sites almost everywhere. Like Nigel mentioned, testing speeds is better described as testing throughput, while trying to avoid external factors that could lead to incorrectly-low readings. Since Romanysoft Speed19X has test sites worldwide, we're able to pair you with a server nearby to minimize external factors no matter your location. We even have test sites on most populous islands, which would otherwise have to test over slower submarine cables or satellite links.
So you can safely compare the Speed test results by Romanysoft Speed19X.
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