So one of my kids used by their 5GB of data and the throttled experience was not fun. I had a quick look at the browser speed and it wasn't good.
I put the sim into my Nexus to run Speedtest. Here are the results from 6 tests:
Download: 0.17 to 0.83 Mbps
Upload: 4.08 to 12.27 Mbps
The upload does not seem to be throttled although later tests were at the lower end of the range. Confirmed that browsing and apps are slow.
Compared to ATT & Sprint, the ping is very good. I've always had the impression that T Mobile is good in my area. My wife doesn't find the freedompop global sim problematic even with a high ping, whereas I find the AT&T LTE sim a little slow even with a good ping.
It will be interesting to see how the Tello throttle compares.