im the only one who uses this radioactive armatar - probably it was removed from the catalog two years ago because no one else took it. this means anyone can easily find what did i say in chatrooms
btw, it isnt a good idea to pick a shield as the armatar if u are joining live chat often. shields are default armatars, this means if u didnt change ur armatar after creating ur account, it'll be a good chance that u find someone using ur armatar when u enter a chatroom
probably it was removed from the catalog two years ago because no one else took it.
The armatar you're using is a seasonal from 2014. Seasonal armatars become unavailable after the current season, though some seasonals come back in future editions of the same seasonal contest.
As for changing out of a shield armatar, an added benefit is the Armatar Exchange quest, which is one of the website quests.
My current armatar is quite easily obtainable and as of now 296 people have earned the quests that unlocks the BTD 5 armatars. I have yet to see anyone else using it but that just maybe my lack of time on the forums.