With Cloudflare I'm guessing it's a more balanced measure.
The other side of this is why Netflix created Fast.com in the first place: ISPs throttling Netflix traffic (or just having poor peering arrangements that affected it) and blaming Netflix when customers complained about poor video quality (due to Netflix downgrading when experiencing congestion) because some speedtest (that likely the ISP prioritized, or at least knew it had better peering to) gave good numbers.
> With Cloudflare I'm guessing it's a more balanced measure.
Both serve the same purpose for their respective owners: to get good scores on fast.com an ISP can't throttle (or allowed to be throttled by avoidable congestion) Netflix traffic, to get good scores on speed.cloudflare.com they can't throttle (or allowed to be throttled by avoidable congestion) traffic to/from Cloudflair's topologically local DCs.
From a user's point of view using both, plus other tests, gives most meaningful results overall.
It's hard to guesstimate the exact bandwidth of the data that arrives in your browser because of differences in protocol, MTU, header compression and all that nonsense, especially over technologies like WiFi. In my experience, the WiFi throughput numbers seem spot on.
Their compensation makes for some hilarious statistics, but when you're downloading more than 200mbps the fast.com speedtest doesn't make much sense anyway. No way in hell is Netflix going to allow your single home internet connection to somehow pull in a full gigabit of streaming video. If you're your own ISP you can make it happen, but on the other hand you'll probably also know how to get statistics directly from your network hardware, in which case the fast.com numbers are useless but it still becomes a useful way to spike the load.
Netflix's speedtest is mostly reliable for what it's meant to do, which is solve the question of "my internet is fast but Netflix keeps buffering".
Edit: another factor to consider is that accurate timing has been disabled in most browsers because of side channel attacks like SPECTRE. It's possible that those are affecting your measurements at very high speeds.
And of course, I'd not expect them to want me to pull down 1gbps of streaming video. But I would expect them to burst my connection when downloading videos for offline viewing, their own bandwidth permitting. Unused bandwidth at a point in time is wasted bandwidth. But more central to my original point, I'd also expect their browser-based speed test to not claim I'm going faster than is physically possible. Let's be honest - however they're measuring the actual connection speeds is not as accurate as some of the alternatives on the same playing field.
Well, Europe has lots of different countries and I've definitely been in countries that are considered to be in Europe where it's not equally fast, and using a VPN can speed up a lot of things.
I would be curious about concrete examples in Europe, though