Our kids football club play on a 3g park that doesn't have holes for corner flags and we were due to play a home Scottish Cup tie where the rules state we had to have corner flags. These bases were to solve that issue, but the flags kept blowing over all game long. These may be suitable for indoor pitches or something but they aren't great for outside - still it kept us compliant and saved us from a possible challenge.
...it doesn't look solid. I suspect that in a few months I may have problems with the ball joint. The bracket isn't as sturdy as previous ones I've had but it doesn't rattle - like the last one did at the end of it's life - and it holds my HTC One