I've never tried clenbuterol, much to my dismay. I have however used albuterol, and did not notice any results.
I tapered up to 4mg e.4.h. I ran it in conjunction with a caloric deficit, and did fasted morning cardio after I could feel my first dose kick in. My reasoning was, mobilized fatty acids from an overnight fast in conjunction with heightened beta oxidation aught to get me swole as bro, or so I had read.
I took the albuterol for two weeks during my last two weeks cutting, without the use of other pharmaceuticals.
I did not notice any results greater than what I was achieving prior to commencing the albuterol. Who knows if comparing it to a placebo would have revealed me losing a greater, statistically significant portion of fat, but I sure as fuck did not notice anything. Just made it harder to write with a pen for two weeks.
Admittedly, not the most helpful post as I cannot offer a comparison with clen, but my anecdote asserts that albuterol is poo.