I was just curios as my friends ORBI also has it built in and every time I test it on his it matches.
This kicked in some curiosity, and your friends router is same as yours? If not what does he have? Same setup more or less? Same WAN connection speed as your friend/service?
Those may matter somewhat, just out of curiosity.
The speedchecker feature is a external service to DD-WRT so YMMV.
FYI here on RT-AC68U WAN Speed is way off, not even close to even single connection tests equivalent to speedtest.net, in fact speedchecker service was 15% correct here.
Short answer: We have the same WAN connection.
My friend has an Orbi RBR50 and 3 sats. I have a EA6900 and two EA6900 APs. I also have two Nanostation Loco M2s which I use as a bridge from my house to his house which is only a couple house down from mine and use his internet for the cost of looking after his house since he is never home (he has many places he uses) and only has internet for looking at his Arlo cameras which I installed.. I am basically his IT/AV guy so I have access to all his electronics. We just got fiber optical installed in our new development and I talked him into upgraded to a 30/30 plan. So I check the speeds on both his router and my router and I also do speed tests between my two Nanostations to see how well everything is working and also to see how the speeds are here in this town. Jardin Colombia is not near any major city. Power/Water/Internet do have a tendency to go out here as we are high in the Andes Mountains and landslides are very common during the rainy season.