There should be a rule that you should know the difference between a counter and a check before being allowed to post things like this.
252 Atk Pure Power Mega Medicham Psycho Cut vs. 124 HP / 0 Def Talonflame: 253-298 (77.1 - 90.8%) -- guaranteed 2HKO
252 Atk Pure Power Mega Medicham Drain Punch vs. 124 HP / 0 Def Talonflame: 135-159 (41.1 - 48.4%) -- guaranteed 3HKO
252 Atk Pure Power Mega Medicham High Jump Kick vs. 124 HP / 0 Def Talonflame: 234-276 (71.3 - 84.1%) -- guaranteed 2HKO
252 Atk Pure Power Mega Medicham Ice Punch vs. 124 HP / 0 Def Talonflame: 181-213 (55.1 - 64.9%) -- guaranteed 2HKO
Talonflame is literally able to come in on anything Medicham can throw besides the rare Thunderpunch at least once; making it a very reliable check. God forbid a player *gasp* predicts the right move and switches Talonflame in on a Drain Punch before proceeding to OHKO it with Brave Bird.
You can't use the "Oh I'm just going to switch out herp derp" argument because I can easily say that I'll use prediction. Nothing useful comes out of the argument. What is certain though is that Talonflame is a reliable check to Medicham (and a good portion of the OU tier atm) and can reliably come in and revenge kill Medicham.
If Stealth Rock is up, Talonflame can't come in on any of those (except Drain Punch.) There's also the fact that Talonflame can't come in on Thunder Punch. Talonflame is NOT a counter to Medicham, it's just not, it can't come in if SR is up and it can't come in on one of Medicham's common coverage moves. It's only a reliable check.
It will also lose 26% of its health in recoil if it uses brave bird.
It's the third most common move... and under half of the Medichams on the ladder even have HJK. And a third have fake out. It's actually sort of depressing.