They seem too good to be that cheap, I've never really used anything by counterfeit but every part I've ever had by Alienation has been absolutely perfect
I used to have working leg like you, then I took a stem to the knee.
That seller has over 17,000 sales with a 99.8% positive feedback. Im betting all its safe to say its a legit deal. 236 sets have also already been sold. This shop has been in business on ebay since 2006
As for Counterfitt, they UK based BMX parts company, specializing in wheels and affordable but quality parts.
REFS-
Vital- KyMike, FEDEXdoobie, adrenalinebmx ,MaximusBikes
Bmx-forum-Tumitama, archerbiker9(2x), mrsanchezz, nguyenna, JoeyBones, fast-and-loose and many others
Also multiple sales on global-flat.com and PinkBike. Theres to many to list all. Most sales are done through texting I havent been able to keep track of who is who.
Actually legit, counterfitt are bmxcity.co.uk 's in house brand, basically made in taiwan catalog parts quality made at knock down price as there is no middle man, also since they are going out of business everything is liquidation phase.