Do you have a "3G" plan or a "4G" plan? A speedtest with a "4G" plan is more of a concern than a "3G" plan depending on how many GB are included in your plan data alottment. If I do conduct a speedtest I usually use ookla....and it will use on average between 30mb and 40mb on a "3G" plan (4G LTE throttled to 3mbps) so a speedtest using a "4G" plan will use about 30× as much data if you are getting up to 100mbps data speeds. If you are really curious then wait until day 30 of your cycle when you may have extra data left in your plan that you would likely not use before renewal. Just ensure you conduct any speedtests before midnight eastern when your plan data counter resets. Additionally as I once was advised by @gpixel you can start the speedtest to see the peak of the data speed and then stop the test before it completes to conserve the amount of data used in the test.
Customers should know that the above app can use hundreds of megabytes (or sometmes more than a gigabyte) of data within seconds. The faster the speeds, the more data this test uses.
Bear in mind, though, doing this will consume 50-100 mb of your plan data. Also make sure you're not in a Wi-Fi area when doing to get a true data speed. Best to toggle Wi-Fi off.
