Well I can't believe Bitcoin cost around £500 per 1 Bitcoin only a couple of years ago and it's current price is £11663 at the time of writing, if you went back further it cost peanuts. There was a time when it halved it's value around 3 years ago, but if people who lost money in the short term continued to be patient they still made a fortune. It's a gamble buying it though, a Bitcoin could be worth £100,000 in a couple of years or it could be worth £500 again.
The big downside is you must be very careful with Bitcoin as there's far too many scams around where people are parted from their money and since it's like using "cash" there is often no come back.
The other downside is Bitcoin and other crypto currencies are a great way for criminals to launder money since it's difficult to trace, authorities have clamped down somewhat making people use ID to purchase them in most cases, but it still happens and it's also the currency of choice for illegal transactions online (E.g. buying illegal drugs, stolen credit cards, counterfeit money, dodgy ID Etc. on the dark web, and even to purchase hosting for illegal websites) and this unfortunately means that a higher proportional of criminals have been made rich by the huge increase in Bitcoin value which is very bad news. It's also a sore point that it's very difficult to buy or sell bitcoin without photo ID because in the UK the only photo ID is a driving licence or passport, millions of people in the UK don't drive and don't travel abroad and are unable to buy or sell them except in higher risk places where there's more chance of being scammed.
Edit:
Also watch out for
Bitcoin miners or other crypto currency miners that use your processor and/or GPU time to make someone else a considerable amount of money when installed on masses of PCs without the owners even realising it. Often these are installed like malware or bundled as an unwanted extra along with other downloaded software, for instance an official version of
uTorrent, a very popular BitTorrent client came bundled with such a miner until masses of people complained and they later removed it. What is worse is they have now found a way to embed crypto currency miners on normal websites which simply run from your favourite browser without your permission when you visit the site, usually without notification. The downside of running such a miner on your PC is it can use up to 100% of your CPU and/or GPU time while making other applications run very slow, it also greatly heats up components where you will often hear your cooling fan speeds increase, but much worse if a PC has poor cooling it could potentially cause critical damage, especially with long term use and there is also the potential to reduce component life, and I haven't yet mentioned that your PC will use considerably more electricity at your expense (running a Bitcoin miner yourself is no longer worthwhile as it often costs more just in electricity than what you will make, that's why dodgy people will trick masses of users into running them on their PCs instead, all earning them money at once making the total considerable while costing them nothing in electricity or hardware costs). So far you will only find web based crypto currency miners on less than reputable websites as far as I know, a common one is websites to freely watch copyrighted TV / movies, another one to look out for is some public torrent sites. You could start seeing them on more websites in future however instead of, or as well as Ads, reputable sites however should always ask your permission first. I hope they incorporate better detection into anti-malware software as at least recently they didn't detect browser based miners, as far as I know these miners currently only thrash your CPU, not the GPU and the miner will stop as soon as you close the website (you can check your CPU usage in Task Manager by pressing the CTRL+ALT & DEL keys together).