I have just upgraded my broadband to 150mbps with BT. I have four deco M5s expanding the Wi-fi throughout my home. I have done a test speed check via the deco app and this shows 146mbps which is fine

When I use the Speedtest via the app it shows over 100mbps but when I use a speedtest via a web browser it only shows around 50mbps.. which one is correct? Why does it show different speeds? thanks