Clen is ok. I don't dislike clen the way some do, possibly because I ran it at a lower dose.
I see no reason to run clen higher than 60-80 mcg. Many think that's too low. Well, I would argue that running it any higher, not only are you asking for sides, but you're asking the drug to do too much of the work for you. Meaning, 60-80 will give you a nice boost, so take the boost and go to work. Don't crank your dose so high that your body thinks its in a triathlon when your actually watching the Simpsons and eating Cheetos.
Eventually, 60-80 mcg loses its boost and that's when most begin dosing up. Well, I believe that's a good time to take a break, not up the dose. Take a couple weeks off or rotate clen with something else and come back in a couple weeks and keep the dose low and safe.
Also, although clen reportedly has a long half life, myself and many others find that it takes effect quickly and winds down throughout the day. I only had problems sleeping the first few days. Sometimes, my wife and I would dose clen first in the am and then a second dose at lunch and it would still wind down in the evening.
The only sides I experience with clen is that it (and other stims) can irritate the prostate, especially with DHT type AAS.
I don't mess with clen anymore as I feel T3 is a better and safer option.