Except they're only worth anything if you cash them out into fiat (if you can). Which apparently isn't always easy, with some exchanges not allowing cashing out to fiat.
And that brings us to another point... there are crypto coins being "invented" every single day (almost). Many are just copy/pasting Litecoin (etc) code and changing a couple vars in the source. Heck there was a 12 year old in the news recently for doing just that, and "inventing" a new coin.
They can't all be "worth" something; they can't all end up as viable currencies. There are hundreds of altcoins already. Some have already failed; indeed some crypto projects have been funded and then collapsed, with investors losing everything. Quite recently in fact. Others will be valueless in the long term, or never attain any value in the first place.
Yet many, many people are mining these worthless coins in the hope that they become valuable. At which point the theory is they will have mined thousands of them and thus be millionaires.
Beyond that, as you just said, the "worth" of the coins can fluctuate wildly between starting a post and finishing it. They are bloomin' useless as actual currencies, and most people who accept money in exchange for goods or services no longer accept any kind of crypto. That's just fact. Let's not forget that people have already lost vast sums the last time crypto "crashed", and the evidence suggests it will continue to overshoot in both directions, reaching highs and then crashing to new lows. If you "hodl" you always run the risk that the price tomorrow crashes to a point where you've lost money, either in buying currency or in buying hardware.
Which suggests that they very much are a ponzi scheme as (many) economists have come forward to suggest. A ponzi scheme based on "pump and dump" principles, and of evangelising crypto to get injections of cash from newbies. Of course miners/crytpo advocates don't trust bankers or economists or the established world order. Unless they're cashing out their *coins into fiat. You know, to actually have something they can use to buy things.
The whole thing is purely a vehicle for speculators, traders, and fraudsters. As currencies these are non-starters. You can't spend them for starters! Only turn them to fiat.
But assuming you do manage to cash out into fiat (which is actually worth something), then so be it. I still wouldn't get into crypto even if you could guarantee I'd make the sorts of figures you're suggesting (although I'm afraid I'm incredibly dubious that you made £11,000+ in three months with 25 cards. Beyond dubious.).
e: Looking closely at MSR it perfectly encapsulates the joke that is crypto.
8 Feb: "worth" 7c ($0.07)
14 Apr: "worth" 20c
28 Apr: "worth" $2
1 May: "worth" $1
Crazy. MSR is obviously a fairly new coin (I've never heard of it). OK, here it is, "invented" Sep 2017. Price until very recently: a few cents.
So you've done exactly what I described above. Mined a new coin that was valueless in the hope that it gained value. Some speculators came along and "pumped" this new altcoin to $2, at which point they all sold and the value crashed back to $1.
This isn't clever, it's manipulating hype. Pump and dump. Coin will probably be worthless in the long run, along with most of the others.
I've read a fair bit about crypto. Mostly on its negative qualities, which is not something miners like to talk about. I actually have a fairly decent grasp on what's going on here, and it's not virtuous. It *is* a get rich quick scheme, and it *is* based on making money by having a few winners and a lot of losers who get left "holding the bags" to use the lingo.
e2: It's basically the stock market on steroids, with volatility levels that are off the charts. But unlike stocks and shares in companies producing useful outputs, crypto is a worthless "token" that only has a value if we attach a value to it.
