It seems @TomjNorthIdaho's server has some issue at the moment. Plus if you try too often, it won't let you connect for next 24 hours. So I'd suggest to post a question in the related topic
The other server by @Martoo
and yet another one by @Garrison1701
were both up at the time I was testing minutes ago.
If you are geographically distant from those servers, don't forget to use UDP, and even that way the results may be affected by some bottleneck on the path which is not related to the transit circuit you verify. Plus I'd recommend to run /interface monitor-traffic
while running the btest, to see the total amount of traffic coming in if you'll run the btest while other data flow through the same circuit. There is no such possibility for traffic being sent through the circuit from your end, unfortunately.
And don't forget all those servers are run by enthusiasts as a gift to the community, so it would be unfair to require a five 9s availability.
You can use a commercial service like speedtest.net instead (commercial = sponsored by advertising), but you'll need a PC as the test client. The advantage is that it suggests geographically near servers, so the results are not that affected by overseas links.