I'm about to start a cycle and will be using a T3/Clen combo. As for the T3 or T4...just read their profiles. You're not gonna mess anything up if you do it right! Just stagger up and back down. Sure you might mess yourself up if you don't stagger back down (which even that is debatable by many), but if you do it right then you'll be fine. To say "don't mess with you're thyroid if you don't have to" is the same as a freakin conservative saying "don't mess with your balls if you don't have too" in reference to test. Just like you could mess yourself up if you don't have a good PCT after a test cycle. Or lets say you take 1000 mg of clen all at once...guess what??? You'll probably DIE. So point is...read up...do it right. Have your doc do some Thyroid test, and if you're good, and the bro's on here have given you solid advice on your cycle give it a try!
My advice would be to try both and see which gives you better results. T4 effects your thyroid...clen effects your beta 2 receptors. They both do different things so it won't hurt to run them together or if you're running the 2 weeks on 2 weeks off approach on the clen to maybe mid cycle throw in the T4 and see what kinda results you get!
Just a little extra info on T3, and of course we all know T4 is the lesser of the two.
http://www.steroid.com/Cytomel.php
Here's a quote:
"Finally, I would like to address the issue of recovery of your natural thyroid function after you stop taking cytomel. The horror stories of people on permanent thyroid replacement just aren´t true. I remember a few years ago, the rumor was circulating that the current Ms.Fitness had permanently shut off her thyroid gland, and was now fat and on thyroid hormone permanently. This is just another horror story based in nothing but conjecture and rumor, the studies I´ve looked at have shown people recovering their thyroid hormone relatively quickly (within months, at most) after going off of several YEARS (!) of thyroid replacement therapy (10)(11). I speculate that you can optimize your metabolic rate with Cytomel for 9-10 months a year, and just normalize yourself for 2-3 months (perhaps the winter, when you are mostly covered up), and then go right back on. Some people in the studies I read were on T3 for 30 years and recovered their natural thyroid function within short order. I think we can safely spend an athletic career using Cytomel 9-10 months out of the year, and just taking those few months off to normalize ourselves. Is this aggressive? Yes. Is this unsafe? NO."