Not a good sentry breaker. Why? Because of its fixed strength.
Is it worth it? Maybe, with the right tools. But those tools must be useful for your other breakers. Otherwise, it is not worth it to have multiple tools to fix only one breaker.
What are those tools? In faction, you have Leech and Ice Carver. Both of which lower the strength of the ices. Those will help you get the sentries to a strength of 3. It will only cost you in additional creds and clicks to install those. This means that it cost you at around , 4 and 4 to make Mimic work, if you use Leech. But Leech will be usefull for Buzzsaw and Cleaver. Once setup, anarch become very efficient at breaking ices, just like shapers.
Out of faction, you can use Dedicated Processor or Takobi. The former being better than the latter. But it is not as efficient as using Leech and Ice Carver.
Of note, Injection Attack is useful here, while you are trying to find your combo cards. There are very few sentry above a strength of 5 (Hydra ,Trebuchet and a stacked Surveyor are the most notables).
Considering that Echelon and Na'Not'K cost 1 influence, you must need your influence greatly to not use those breakers (there is also Carmen at only 2 influence). But if you use only anarch breakers, using the aforementioned tools will let you be efficient in breaking ices (while being somewhat slow to setup). This is why Mimic is unlikely to be used out of faction.
It is a bit sad that this breaker has such drawback, because the art and quote are very cool. Still, is has its place.
As one of the old guard, it's fun to see how perceptions have shifted. In the early days of Netrunner, Mimic was undeniably the best Killer in the game. Before Mongoose, we really didn't have any good options to break sentries besides Mimic and Faerie. And now we have Bukghalters and Carmen and Nanotk and their ilk, spoiling us for choice...— HolyMackerel