I chose the A5 size as best suited to my needs but if you are not using it for more than shopping lists or short memos the A6 would be easier to keep in your pocket.
The only drawbacks are very minor. The instructions suggest that notes should not be kept on the padfor more than 1 month as the ink is less fully erasable after this time and may leave permanent marks on the page. Also I have no local supplier of Pilot Frixion pens so will have to send away for some but will take the opportunity to get blue and red anyway as they are easily found on Amazon or other websites. Perhaps a loop to store the pen on the notebook would be helpful.
Altogether a handy piece of kit, robustly made but slightly expensive albeit well presented with everything you need.