My opinion is based on my own personal experience and I have no medical training at a level above VTCT level 3 sciences. But I do know my own body well and I have read everything thyroid related constantly since diagnosis in early 2012.
When first diagnosed hypo and treated I responded well to T4 and it made a huge difference to how ill I had been, however there were still lingering problems... some muscle aches, restless legs, weight gain.
In January 2014 I tried a little more T4, going below TSH of 1 (0.2) and still had the muscle aches, restless leg, weight gain problems and now with the addition of diarrhoea and constant headaches and insomnia. I got a ticking off from my GP and I had to agree that the experiment with more T4 had not been successful. I went back to my prescribed T4 dose and the headaches/diarrhoea/insomnia went, my TSH level rose to 1.91, but I still had some muscle aches, restless legs, weight gain.
I did a lot of research into T3 and so many times read about people who had depression which was ONLY resolved with the addition of T3. I didn't have depression but I did have other issues which seemed unresolvable on T4 only even when I upped the T4 dose.
After four weeks back on my regular dose of T4 I added a 6mcg dose of T3 in the morning and another 6mcg T3 dose in the evening. I began this in April and it worked almost immediately. I have not had a return of the diarrhoea/headaches/insomnia and have also lost the muscle aches, stopped the awful night-time restless legs, stabilised my weight and I've even lost a few pounds. I have had NO symptoms or signs of going hyper or having too much thyroxine.
For the first few days about two hours after I had taken my T3, I had a faster resting pulse rate (RHR: 80-86 beats per minute) for an hour or so, then it settled back to around 62bpm. My usual RHR is around 62bpm. This morning, nearly two hours after my T4/T3 morning dose, my RHR is 63 and for a long time, taking the T3 has not caused my pulse rate to rise in the few hours after taking it.
I'm settled on my new regime (four months now) and would never willingly go back to T4 only. I can't give you a current TSH as I've not been summoned yet for another test and I'd rather not 'fess up for the time being 
. I'll face that battle when I'm next summoned - hopefully not until early2015... I don't think my decision to self-medicate and add T3 will go down too well and if I can avoid owning up to it I will. It puzzles me why T3 has such a public bad press - many doctors privately acknowledge that T3 is actually very helpful for many. I suppose within the budgets of the NHS, the convenient little TSH test is no longer as useful once T3 medication has been added into the mix... although I have learnt in the past few years that actually the TSH test was never so great anyway.
My conclusion; whilst I was converting T4 well, it seems that T3 reaches the parts T4 cannot or that T4 cannot sustain consistently. I don't know why, it just does.
Will I go back to T4 only? Not if I can help it!
Taking T3 only T4 low
Should I increase my T4 or stop T3
Adding T3 or T4 to NDT
Which to reduce, T4 or T3? 
