Couple of thoughts, gotta hype the British show "Detectorists" if you can get episodes on Netflix or some such. Also concerning "Redbooks". I have a 1974 and a Professional Edition (2011) I bought from someone on Craigslist for $5 and don't feel a burning need for others, considering it is more an informational guide more than anything else. If you can buy a used one, go for it.
If you get a chance, compare the 2 and see which you like better. Professional edition is not much more expensive than the regular red book. Mega Red is quite a bit higher. Just food for thought.
It works better in countries like the UK, where they have old coins that are magnetic, but it is fun. My magnet goes where I go in the trunk.