another fitbit/pedometer question...!

I really like the idea that a fitbit calculates your tdee every day. However I dont much like the idea of spending a small fortune on a gadget I may be able to manage without. I have a polar f6 for measuring dedicated workouts and a decent omron pedometer which tells me calories burned. I just cant work out how this could fit in place of a fit bit.

Should I add the calories burned from my pedometer to my bmr to get my days tdee? Or would this fall a bit short still as I don't think it picks up all the time I am on my feet taking short steps around the kitchen etc. I am certainly not bei g sedentary then, but I think the pedometer only starts registering after 4 seconds of continuous walki g.

And if it really is better/more accurate to use a fit bit, is it really worth the extra for a fitbit one rather than zip?

Thanks in advance!