Reduced residue left in the stove was from the Esbit ones, especially compared to Hexy blocks, many different ones to try including even Barbequeue lighting blocks.
From the esbit marketing bumph :- "Esbit fuel tablets differ from most other solid fuel tablets in that they are non-toxic and completely consume themselves when burned. Most other fuel tablets leave a toxic residue behind. Esbit fuel tabs can be safely burned inside a properly ventilated room."
I would def recoment a little bottle of meths and a can stove over using solid fuel tabs anyday though.