You can't say in truth that there are no disadvantages to ANY system, that is a form of bias
A disadvantage of Bitcoin is: Confirmation time of 10 minutes would greatly slow checkout for large purchases in shops, risk of double spending if they left the store instantly is high.
Small block size inhibiting transactions, transaction fees too high for 'cup of morning coffee' purchases in fact higher than many bank fees for some transactions (BCH, LTC and NEM attempts to solve this).
The need for users to be responsible with their keys, which most will not be. A few in my college laugh at me for the idea of hardware wallets yet keep £4 - 5k on an exchange wallet.
There are many advantages too, such as trustless, no censorship, essentially digital cash, no worry to the merchant about chargebacks (as an online shop, i closed shop due to this very problem, even a single customer charging back can cripple the cashflow of a small business. I for one as a merchant would love irreversible transactions, just like cash, provided you can trust the merchant. For speed of confirmations, though Litecoin and NEM are superior in this regard. For throughput, BCH is.
The scaling problem is going to cause problems as there is no simple solution. Do we want the blockchain as a worldwide payment system or a settlement layer? Try processing the volumes of visa and mastercard using the bitcoin code, and you may just find blocks of several hundred megabytes, the blockchain size would be insane, leading to the need to somehow prune it.
Unstable price is a current disadvantage, too. I personally think the most stable asset to secure assets is silver, gold being at an all time high, higher than platinum and bitcoin all over the place. If your your average Joe blogs, the safest investment is a permanent roof over your head = home ownership. Whatever the fluctuations in the housing market, once its paid, THAT is your security.
Bitcoin is good as part of a diverse portfolio, however. Certainly gave me a better return than savings in a bank
Another downside is always focusing on the 'community' aka forums surrounding a coin and decisions which are made, when practically 99% of users won't even touch a forum about their currency, they want to use it as just that, a currency. Most who use it havn't a clue how it works, be it the fiat banking system, or Bitcoin. Wallets and systems will need to make it easy and simple to use, and secure. Using a secure enclave on modern devices to store keys is a must.