Hi. Have been using a block for about 3 years now and have of course eventually dropped it a few times. No probs, still useable but looking to get another. I cannot remember where I got the existing one but I know it was cheap and it does what it is meant to do. Looking now, it seems it is a bit of a minefield in that many are around £4/5 and indeed a lot more are silly money upwards. The likes of Osma etc seem popular but............. there are several places where I can get a 100g block for around £1.60 delivered. Question is - are there inferior versions of these to particularly look out for? Different types maybe too eg magnesium / aluminium/ potassium etc etc. OR is alum simply alum and the cheapies are just as good?