The first occurence of the Speedcheck speed test in the WayBack Machine is June 2018.
Speedcheck is a miscellaneous speed test. When testing with 75 Mbps the speed test should be categorized as conservative, however with 100 Mbps Speedcheck should be categorized as ambiguous or realistic.
Speedcheck is slightly to slow to met the 30 seconds knockout criterion. Hence this speed test is not recommended.
Speedcheck is the only speed test which measures the stability of the download and the upload speed.
In the speed test overview you find all findings regarding the Speedcheck speed test.